Hemmeligheten til å finne fortjeneste i parhandel. Quants er Wall Streets navn for markedsforskere som bruker kvantitativ analyse for å utvikle lønnsomme handelsstrategier Kort sagt, en kvant kammer gjennom prisforhold og matematiske forhold mellom selskaper eller handelsbiler for å divinere lønnsomme handelsmuligheter I løpet av 1980-tallet ble en gruppe kvelder arbeider for Morgan Stanley slo gull med en strategi som kalles parhandel Institusjonelle investorer og proprietære handelsdisker hos store investeringsbanker har brukt teknikken helt siden, og mange har gjort et ryddig fortjeneste med strategien. Det er sjelden i beste interesse for investeringsbanker og fondsbestyrere å dele lønnsomme handelsstrategier med publikum, så parhandelen forblir en hemmelighet for proffene og noen få deftige individer fram til adventen av internett. Online trading åpnet lokket på sanntid finansiell informasjon og ga nybegynnere tilgang til alle typer investeringsstrategier Det tok ikke lang tid før parene handlet til attra ct individuelle investorer og småhandlere som ønsker å sikre deres risikoeksponering mot bevegelsene i det bredere markedet. Hva er Par Trading. Pairs trading har potensial til å oppnå fortjeneste gjennom enkle og relativt lavrisikoposisjoner Parhandelen er markedsneutral betyr at retningen til det totale markedet ikke påvirker sin gevinst eller tap. Målet er å matche to handelsbiler som er svært korrelerte, handle en lang og den andre kort når parets prisforhold avviger x antall standardavvik - x er optimalisert ved hjelp av historiske data Hvis paret vender tilbake til sin gjennomsnittlige trend, gjøres en fortjeneste på en eller begge posisjonene. Et eksempel ved å bruke Stocks. Traders kan bruke enten grunnleggende eller tekniske data for å konstruere et par handelsstil. Vårt eksempel her er teknisk i natur, men noen handelsfolk bruker et PE-forhold eller andre grunnleggende faktorer for å måle korrelasjon og divergens. Det første trinnet i å designe en parhandel er å finne to aksjer som er svært korrelerte d Vanligvis betyr det at bedriftene er i samme bransje eller delsektor, men ikke alltid. Eksempelvis kan indekssporingslagre som QQQQ Nasdaq 100 eller SPY SP 500 tilby gode parhandelsmuligheter. To indekser som generelt handler sammen, er SP 500 og Dow Jones Utilities Average Denne enkle prisplottet av de to indeksene viser deres sammenheng. For vårt eksempel vil vi se på to virksomheter som er svært korrelerte GM og Ford Siden begge er amerikanske bilprodusenter, har deres aksjer en tendens til å bevege seg sammen. Below er et ukentlig diagram over prisforholdet mellom Ford og GM beregnet ved å dele Ford s aksjekurs ved GM s aksjekurs Denne prisforholdet kalles noen ganger relativ ytelse, ikke forveksles med den relative styrkeindeksen noe helt annerledes. Den midterste hvite linjen representerer det gjennomsnittlige prisforholdet de siste to årene De gule og røde linjene representerer ett og to standardavvik fra middelforholdet, respekterer y. I tabellen nedenfor kan potensialet for fortjeneste identifiseres når prisforholdet treffer første eller andre avvik. Når disse lønnsomme avvikene oppstår, er det på tide å ta en lang posisjon i underpresteren og en kort posisjon i overkassen. Inntektene fra den korte salget kan bidra til å dekke kostnadene for den lange posisjonen, slik at parene handler rimelig å sette på. Størrelsen til paret skal matches med dollarverdi i stedet for antall aksjer på denne måten en 5 trekk i en tilsvarer en 5 trekk i andre Som med alle investeringer, er det en risiko for at handelen kan bevege seg inn i det røde, så det er viktig å bestemme optimaliserte stopp-poeng før implementering av parhandelene. Et eksempel ved bruk av Futures-kontrakter. Parhandelsstrategien fungerer ikke bare med aksjer, men også med valutaer, varer og til og med opsjoner I futures-markedet er mini kontrakter - mindre kontrakter som representerer en brøkdel av verdien av fullstørrelsesposisjonen - muliggjør mindre investorer å handle i futures. En parhandel i futures markedet kan innebære en arbitrage mellom futures kontrakten og kontantposisjonen til en gitt indeks Når futures kontrakten kommer foran kontantposisjonen, kan en næringsdrivende prøve å tjene ved å forkorte fremtiden og går lenge i indekssporingsbeholdningen, og forventer at de kommer sammen på et eller annet tidspunkt Ofte er bevegelsene mellom en indeks eller vare og futureskontrakten så stram at fortjenesten bare er igjen for de raskeste handelsmennene - ofte bruker datamaskiner til automatisk å utføre enorme stillinger ved et blink av et øye. Et eksempel ved å bruke Options. Option handlerne bruker samtaler og setter for å sikre risiko og utnytte volatilitet eller mangel derav. Et anrop er en forpliktelse fra forfatteren til å selge aksjer av en aksje til en gitt pris en gang i fremtiden Et put er en forpliktelse fra forfatteren til å kjøpe aksjer til en bestemt pris en gang i fremtiden. Et par som handler i opsjonsmarkedet kan innebære å ringe for et sikkerhet som overgår det ir en annen høyt korrelert sikkerhet og samsvarer med stillingen ved å skrive et sett for paret, den underpresterende sikkerheten. Da de to underliggende posisjonene går tilbake til deres gjennomsnitt igjen, blir alternativene verdiløse slik at næringsdrivende kan lomme inntektene fra en eller begge posisjonene. Bevis for lønnsomhet. I juni 1998 utgav Yale School of Management et papir skrevet av Even G Gatev, William Goetzmann, og K Geert Rouwenhorst som forsøkte å bevise at parhandel er lønnsomt. Ved bruk av data fra 1967 til 1997 oppdaget trioen at over en seks måneders handelsperiode, handler parene i gjennomsnitt en 12 retur. For å skille lønnsomme resultater fra vanlig flaks, inkluderte testen konservative estimater av transaksjonskostnader og tilfeldig utvalgte par. Du finner det fulle 34-siders dokumentet her. De som er interessert i parene trading teknikk kan finne mer informasjon og instruksjon i Ganapathy Vidyamurthy s bok Pairs Trading Quantitative Methods and Analysis som du finner henne e. Det brede markedet er fullt av oppturer og nedturer som tvinge ut svake spillere og forvirrer selv de smarteste prognostikatorene. Heldigvis, ved å bruke markedsneutrale strategier som parhandel, kan investorer og forhandlere finne overskudd i alle markedsforhold. Parrets skjønnhet er dens enkelhet Det lange korte forholdet mellom to korrelerte verdipapirer fungerer som en ballast for en portefølje fanget i det hakkede vannet i det samlede markedet. Lykke til med jakten på fortjeneste i par handel, og her er suksessen din i markedene. Maksimum mengden penger som USA kan låne Gjeldstaket ble opprettet under Second Liberty Bond Act. Renten der et depotinstitusjon gir midler opprettholdt i Federal Reserve til en annen depotinstitusjon. 1 Et statistisk mål for spredning av avkastning for en gitt sikkerhets - eller markedsindeks Volatilitet kan enten måles. En akt gikk den amerikanske kongressen i 1933 som bankloven, som forbød kommersiell b anker fra deltakelse i investeringen. Nonfarm lønn refererer til hvilken som helst jobb utenfor gårder, private husholdninger og nonprofit sektor Den amerikanske arbeidsstyrken. Den valuta forkortelse eller valutasymbol for den indiske rupee INR, valutaen i India Rupee består av av 1.A-metoden er tilveiebrakt for å oppfylle en parhandelsforespørsel og inkluderer trinnene å motta et antall parhandelskrav som utfører en transaksjon for en første del av en av flere parhandelskrav og samsvarer med en andre del av den ene av Flertallet av parhandel forespørsler mot en annen av de fleste parhandel forespørsler. 46.1 En datamaskinimplementert fremgangsmåte for å oppfylle en parhandelsforespørsel, omfattende trinnene for å motta en rekke parhandelskrav, omfattende en parhandelanmodning og en annen parhandelanmodning, hvor hver parhandelskode omfatter en forespørsel om handel med en første sikkerhet, en forespørsel om å handle en annen sikkerhet og en forespørsel om å handle den første sikkerheten og den andre sikkerheten med en minimumspersjonsgrense, og hvor den første sikkerhet og den andre sikkerheten hver har en budpris og en forespørselspris. i markedet for den første sikkerheten og den andre sikkerhetsbestemmelsen spør spørsmålet spredes i markedet for den første sikkerheten og den andre sikkerhetsbestemmelsen. Det bestemmes at minimumspredningsgrensen for hvert parhandelsforespørsel oppfylles av et utvalg av budbuds-spredningen og sa spør spørre spredning utføre en transaksjon mellom en første del av handelen med den første sikkerhet i nevnte ene-par-handelsforespørsel og minst en ikke-par-handelsforespørsel, utredet at minimumspredningsgrensen for det ene parhandelsforespørselen er oppfylt av nevnte rekkevidde av budbudspredningen, og spørsmålet spørspredes og samles, ved hjelp av en datamaskin, en andre del av handelen av den første sikkerhet i det ene parhandel forespørsel og i det minste en første del av handelen med den andre sikkerhetsbehandlingen i det ene parhandelsforespørselen mot den andre parbehandlingsforespørsel, forutsatt at et område av minimumspredningsgrensen for det ene parhandelsforespørselen og den andre parbehandlingsforespørsel overlapper med nevnte rekkevidde av budbudet spredt og spørg spørre spredningen. 2. Fremgangsmåte ifølge krav 1, karakterisert ved at trinnet med å utføre en transaksjon for det første parti av handelen med den første sikkerhet i nevnte eneparhandel, omfatter trinnet for å utføre en transaksjon for nevnte første del av handelen med den første sikkerhet i det ene parhandelsforespørsel i et eksternt marked.3. Fremgangsmåte ifølge krav 1, hvori trinnet for å utføre en transaksjon utføres av en finansinstitusjon h avgjøre en ordrebeholdning og trinnet med å utføre en transaksjon inkluderer trinnet for å utføre en transaksjon for den første del av handelen med den første sikkerhet i nevnte ene-par-handelsforespørsel mot ordrefortegnelsen. 4. Fremgangsmåte ifølge krav 1 som videre omfatter. utføre en transaksjon mellom en andre del av handelen med den andre sikkerheten i nevnte eneparhandelskrav og minst en annen forespørsel om ikke-parhandel, forutsatt at minimumspredningsgrensen for det ene parhandelskrav er oppfylt av nevnte rekkevidde av budet budspredning og spør spørsmålet spredes og hvor trinnet med å utføre nevnte første del av det ene parhandelsforespørselen og utføre nevnte andre del av nevnte eneparhandelskrav inkluderer trinnene for å bestemme om budprisen for den første sikkerhet og budprisen for den andre sikkerheten oppfyller en spread limit. determinerer et beløp av den andre sikkerheten som kan selges basert på en budstørrelse knyttet til den andre sikkerheten. beregning av en equiva utlånt beløp av den første sikkerheten som kan kjøpes basert på mengden av nevnte andre sikkerhet som kan bli solgt. justering av tilsvarende beløp av den første sikkerheten basert på justeringskriterier. beregning av en kjøpesum for den justerte ekvivalente mengden av det første sikkerhetsbaserte på spredningsgrensen. eksempel på en initierende rekkefølge for å kjøpe den justerte ekvivalente mengden av den første sikkerheten til nevnte kjøpesum og utføre en deksjonsordre for å selge nevnte mengde av den andre sikkerheten. 5. Fremgangsmåte ifølge krav 4, karakterisert ved at trinnet å utføre en Dekningsordren for å selge inkluderer trinnet for å utføre en deksjonsordre for å selge nevnte beløp av den andre sikkerheten til budprisen for den andre sikkerheten. 6. Fremgangsmåten i krav 4, som videre omfatter trinnene for å bestemme om spørprisen til den første sikkerhet og spørreprisen for den andre sikkerheten oppfyller en spread limit. determinere et beløp av den første sikkerheten som kan kjøpes basert på en tilbudsstørrelse assosiert med den første se curity. calculating en ekvivalent mengde av den andre sikkerheten som kan selges basert på mengden av den andre sikkerheten som kan kjøpes. justering av ekvivalent mengde av den andre sikkerheten basert på justeringskriterier. beregning av en salgspris for den justerte ekvivalente mengden av nevnte andre sikkerhet basert på spredningsgrensen. utfører en initierende rekkefølge for å selge den justerte ekvivalente mengden av den andre sikkerheten til nevnte salgspris og utføre en deksjonsordre for å kjøpe nevnte mengde av den første sikkerhet. 7. Fremgangsmåte ifølge krav 6, karakterisert v e d at trinn for å utføre en dekselordre for å kjøpe inkluderer trinnet for å utfylle en deksjonsordre for å kjøpe det beløpet av den første sikkerheten til forespørselsprisen for den første sikkerheten. 8. Fremgangsmåte ifølge krav 6, karakterisert ved at justeringskriteriene inkluderer en minimumsbeløp og en maksimal beløp. 9. Fremgangsmåte ifølge krav 8, karakterisert v e d at trinnet med å utføre en initierende rekkefølge innbefatter trinnet til å omgjøre nevnte initierende rekkefølge til en rund masse størrelse . Fremgangsmåte ifølge krav 1, karakterisert v e d at trinnet med å utføre en første del av handelen med den første sikkerhet i nevnte eneparhandelforespørsel inkluderer trinnet for å utføre en første del av handelen med den første sikkerhet i nevnte ene parhandelskode i en flerhet av trancher. 11. Fremgangsmåte ifølge krav 1, karakterisert ved at den ene sparselforespørselen har en første spredningsgrense, og den andre sparselforespørselen har en andre spredningsgrense, og hvor trinnet til å tilpasse nevnte andre del av nevnte handel med den første sikkerhet i det ene parhandelsforespørselen og i det minste en første del av handelen med den andre sikkerheten i det ene parhandelsforespørselen mot nevnte andre handelsforespørsel omfatter videre trinnene for å bestemme at et område av den første spredningsgrense og det andre spredningsgrensen begrense overlapper med et markedsperspektiv. sett et spredningsnivå. kalkulere priser for den første sikkerheten og den andre sikkerheten som er innenfor markedet spredt og basert på nevnte spredningsnivå og. matching sagt andre del av handelen med nevnte første sikkerhet i det ene parhandelsforespørselen og i det minste en første del av handelen med den andre sikkerheten i det ene parhandelsforespørselen mot den andre parhandelsforespørsel basert på de beregnede priser.12 Metoden for krav 11, hvor trinnet med å sette et spredningsnivå innbefatter trinnene for å beregne et middel mellom den første spredningsgrense og den andre spredningsgrensen og å sette spredningsnivået som nevnt, hvis nevnte gjennomsnitt ligger innenfor nevnte markedsspredning. krav 12 videre innbefattende trinnet for å identifisere et spredningsbeløp som er nærmest nevnte middel og innenfor nevnte markedsspredning og sette spredningsnivået som nevnte spredningsbeløp hvis nevnte middel ikke er innenfor markedsspredningen. 14. Fremgangsmåte ifølge krav 1, karakterisert v e d at nevnte et par-handelsforespørsel har en første spredningsgrense, et kjøpsforhold og et salgsforhold, nevnte et annet parhandelskrav har en andre spredningsgrense, et kjøpsforhold og et salgsforhold og hvor trinnet med å matche en andre port ion av nevnte handel med nevnte første sikkerhet i det ene parhandelskrav og i det minste den første del av handelen med den andre sikkerheten i det ene parhandelsforespørsel mot nevnte andre handelsforespørsel omfatter videre trinnene for å bestemme at kjøpsforholdet og det nevnte salgsforhold som er knyttet til den ene handelsforespørsel, er ikke likeverdig med kjøpsforholdet og sølleforholdet mellom nevnte andre handelsforespørselsforespørsel og at en overlapping eksisterer mellom området for den første spredningsgrensen og den andre spredningsgrensen og et markedsspredning. at det eksisterer markedspriser som ligger innenfor overlappingen. detektering av et mismatchbeløp i den andre sikkerheten basert på en forskjell mellom kjøpsforholdet og salgssamarbeidet som er knyttet til nevnte eneparhandelskrav og kjøpsforholdet og salgsforholdet mellom det andre parhandel request. calculating et kryssbeløp for den første sikkerheten og den andre sikkerheten. velger en kryssepris for den første sikkerheten og den andre sikkerheten som er innenfor nevnte overlapping. bestemmer at nevnte feilparametre er tilgjengelig ved nevnte kryssepris for den andre sikkerhetsmatching nevnte andre del av handelen med den første sikkerhet i nevnte eneparhandelskrav og i det minste den første del av handelen med den andre sikkerhet i det ene paret handelsforespørsel mot nevnte andre parhandelskrav basert på de valgte priser og utførelse av en transaksjon for nevnte feilparametre av nevnte andre sikkerhet ved nevnte kryssepris for nevnte andre sikkerhet. 15. Fremgangsmåte ifølge krav 14, karakterisert ved at trinnet med bestemmelse at nevnte feilpasningsbeløp er tilgjengelig ved nevnte kryssingspris for nevnte andre sikkerhet inkluderer trinnet for å bestemme at nevnte feilpasningsbeløpet er tilgjengelig i et eksternt marked ved nevnte kryssepris for nevnte andre sikkerhet. 16. Fremgangsmåte ifølge krav 14, karakterisert ved at trinnet med bestemmelse Det nevnte feilparametret er tilgjengelig utføres av en finansinstitusjon som har en ordrebeholdning og trinnet med å bestemme det nevnte feilparametre er tilgjengelig ved nevnte kryssepris for nevnte andre sikkerhet inkluderer trinnet til bestemmelse av at nevnte feilparametre er tilgjengelig i nevnte ordrebeholdning ved nevnte kryssepris for nevnte andre sikkerhet. 17. Fremgangsmåte ifølge krav 1, karakterisert ved at det ene parhandelskrav og nevnte et annet parhandelsforespørsel indikerer et antall sprer og hvor trinnet til å tilpasse et andre parti av handelen med nevnte første sikkerhet i nevnte eneparhandelforespørsel og i det minste den første delen av handelen med den andre sikkerheten i det ene parhandel forespørsel mot nevnte andre parhandelskrav, innbefatter trinnet for å samle en andre del av handelen med den første sikkerhet i nevnte eneparhandelskrav og i det minste den første delen av handelen med den andre sikkerheten i det ene parhandelsforespørsel mot sa et annet par handelsforespørsel dersom antall spredninger er større enn et minimum antall spredninger. 18. Fremgangsmåte ifølge krav 1, inklusiv trinnet for å motta en preferanse for å fylle i det minste noen av nevnte antall handelsforespørsler via utførelsessteget. 19. Fremgangsmåte ifølge krav 1, inklusiv trinnet for å motta en preferanse for å fylle i det minste noen av nevnte antall handelsforespørsler via matchende trinn. 20 Metoden for krav 1 hvor en klient sender en forespørsel angående en status for nevnte parhandelsforespørsel og statusen til nevnte parhandelsforespørsel blir kontinuerlig oppdatert i sanntid.21. Fremgangsmåte ifølge krav 19, karakterisert ved at preferansen blir sendt av en klient elektronisk.22 Metoden i samsvar med krav 1, karakterisert v e d at en klient mottar en simultan rapport når parbehandlingsforespørselen er fylt og klienten bekrefter parmerkelen elektronisk. 23. Fremgangsmåte ifølge krav 1, karakterisert ved at den videre omfatter å utføre en transaksjon mellom et andre parti av handelen med den andre sikkerheten i sa ett par-handelsforespørsel og i det minste en annen forespørsel om ikke-parhandel, forutsatt at minimumspredningsgrensen for det ene parhandelsforespørselen er oppfylt av nevnte rekkevidde av budbudspreda d og spør spørsmålet spredes og hvor trinnet med å utføre nevnte første del av det ene parhandelsforespørselen og utføre nevnte andre del av nevnte eneparhandelforespørsel innbefatter trinnet for å bestemme om spørreprisen for den første sikkerhet og spørringen Prisen på den andre sikkerheten oppfyller en spread limit. determinere et beløp av den andre sikkerheten som kan kjøpes basert på en askestørrelse knyttet til den andre sikkerheten. beregne en tilsvarende mengde av den første sikkerheten som kan selges basert på mengden av andre sikkerhet som kan kjøpes. justering av tilsvarende ekvivalent mengde av den første sikkerhet basert på justeringskriterier. beregning av en salgspris for den justerte ekvivalente mengden av den første sikkerheten basert på spredningsgrensen. utførelse av en initierende rekkefølge for å selge den justerte tilsvarende mengde av sa første sikkerhet til nevnte salgspris og eksekverte en dekselordre for å kjøpe nevnte mengde nevnte andre sikkerhet.24 Et system for å oppfylle et par trad en forespørsel, hvilket system mottar et flertall av parhandelskrav, omfattende en parhandelanmodning og en annen parhandelsforespørsel, hvor hver parhandelsforespørsel omfatter en forespørsel om handel med en første sikkerhet, en forespørsel om handel med en andre sikkerhet og en forespørsel om å handel med den første sikkerheten og nevnte andre sikkerheten med en minimumspersjonsgrense, og hvor den første sikkerheten og den andre sikkerheten hver har en budpris og en forespørselspris, bestående av en parhandelsmotor for å bestemme budbudets spredning i markedet for sa første sikkerhet og nevnte andre sikkerhetsbestemmelse. Spørsmålet spredes i markedet for den første sikkerheten og nevnte andre sikkerhetsbestemmelse. Det fastslås at minimumspredningsgrensen for hvert parhandelsforespørsel oppfylles av et utvalg av budbudspredningen og spør spørsmålet spredt for hver sikkerhet som utfører en transaksjon mellom en første del av handelen med den første sikkerheten i det ene parhandelsforespørselen og minst en forespørsel om ikke-parhandel, forutsatt at mini mum spredningsgrense for det ene parhandel forespørselen er oppfylt av nevnte rekkevidde av bud bud spredning og spørre spørre spredning og. a par kryssing nettverk for å tilpasse en andre del av handel med den første sikkerheten i nevnte ene par handel forespørsel og på minst en første del av handelen med den andre sikkerhetsbehandlingen i det ene parhandelsforespørselen mot den andre parhandelsforespørsel, forutsatt at et område av minimumspredningsgrensen for det ene parhandelsforespørselen og den andre parhandelsforespørsel overlapper med nevnte rekkevidde Det angitte budbud spredte og spør spørsmålet spredt. 25 Systemet ifølge krav 24, som videre omfatter en kobling til et eksternt marked hvor nevnte parhandelsmotor sender fremover transaksjonen for den første del av handelen med den første sikkerhet i nevnte eneparhandelskrav for utførelse i det eksterne markedet via nevnte link.26. Systemet ifølge krav 24, som videre omfatter en finansinstitusjon som har en ordrebeholdning og hvor nevnte parhandelsmotor utfører transaksjonen n for nevnte første del av handelen med nevnte første sikkerhet i nevnte eneparhandelforespørsel mot ordrefortegnelsen.27. Systemet ifølge krav 24, karakterisert ved at parhandelsmotoren bestemmer hvorvidt budprisen for den første sikkerheten i det ene parhandel ber om og budprisen for den andre sikkerheten i det ene parhandelsforespørselen oppfyller en spredningsgrense bestemmer at en mengde av den andre sikkerheten som kan selges basert på en budstørrelse assosiert med den andre sikkerheten, beregner en tilsvarende mengde av den første sikkerheten som kan kjøpes basert på mengden av den andre sikkerheten som kan selges, justerer den ekvivalente mengden av den første sikkerhet basert på justeringskriterier, beregner en kjøpesum for den justerte ekvivalente mengden av den første sikkerhet basert på spredningsgrensen, utfører en initierende rekkefølge for å kjøpe den justerte ekvivalent mengde av den første sikkerheten til nevnte kjøpesum og utfører en deksjonsordre for å selge mengden av den andre sikkerheten.28 Den system ifølge krav 27, hvor parhandelsmotoren utfører en deksjonsordre for å selge mengden av den andre sikkerheten til budprisen for den andre sikkerheten. 29. Systemet ifølge krav 27, hvor parhandelsmotor bestemmer hvorvidt spørprisen på den første sikkerheten og spørprisen på den andre sikkerheten oppfyller en spredningsgrense, bestemmer at et beløp av den første sikkerheten som kan kjøpes basert på en tilbudsstørrelse assosiert med den første sikkerheten, beregner en tilsvarende mengde nevnte andre sikkerhet som kan selges basert på mengden av Den andre sikkerheten som kan kjøpes, justerer det tilsvarende beløpet av den andre sikkerheten basert på justeringskriterier, beregner en salgspris for den justerte tilsvarende mengden av den andre sikkerheten basert på spredningsgrensen, utfører en initierende rekkefølge for å selge den justerte tilsvarende mengden av nevnte andre sikkerhet til nevnte salgspris og utfører en deksjonsordre for å kjøpe det beløpet av den første sikkerheten.30 Systemet med krav 29 hvor parhandelsmotoren utfører en deksjonsordre for å kjøpe beløpet av den første sikkerheten til spørpesummen for den første sikkerheten.31. Systemet ifølge krav 27, karakterisert ved at justeringskriteriene innbefatter en minimumsbeløp og en maksimal mengde.32 Systemet med krav 31 hvor parhandelsmotoren runder den initierende rekkefølge til en rund masse størrelse.33. System ifølge krav 24, hvor parhandelsmotoren utfører i det minste en del av handelen med en av nevnte verdipapirer i en av parhandelskravene i en Antallet av trancher.34. System ifølge krav 24, hvor nevnte eneparhandelforespørsel har en første spredningsgrense, og nevnte andre parhandelsforespørsel har en andre spredningsgrense og hvor par-kryssningsnettverket bestemmer at et område av nevnte første spredningsgrense og nevnte sekund spredningsgrenseoverlapper med et markedsspredningssett et spredningsnivå beregner priser for den første sikkerheten og den andre sikkerheten som ligger innenfor markedsspredningen og basert på nevnte spredningsnivå og matc hes nevnte andre del av handelen med nevnte første sikkerhet i det ene parhandelsforespørselen og i det minste en første del av handelen med nevnte andre sikkerhet i nevnte eneparhandelforespørsel mot en annen av nevnte flertallforhandlingsforespørsel basert på de beregnede priser .35 System ifølge krav 34, hvor parkryssingsnettverket beregner et middel mellom den første spredningsgrense og den andre spredningsgrensen og setter nevnte spredningsnivå som nevnt hvis nevnte middel er innenfor nevnte markedsspredning. 36. System ifølge krav 35, karakterisert ved at Parkryssingsnettverket identifiserer et spredningsbeløp som er nærmest nevnte gjennomsnitt og innenfor nevnte markedsspredning og angir nevnte spredningsnivå som nevnte spredningsbeløp hvis nevnte gjennomsnitt ikke ligger innenfor nevnte markedsspredning. 37. System ifølge krav 24, hvor nevnte eneparhandelskrav har en første spredningsgrense, et kjøpsforhold og et salgsforhold, sa et annet parhandelskrav har en andre spredningsgrense, et kjøpsforhold og et salgsforhold og hvor parets kryssingsnettverk bestemmer at s hjelpekjøpsforhold og det nevnte salgsforholdet som er knyttet til det ene parhandelskrav, svarer ikke til kjøpsforholdet og salgsforholdet til nevnte andre handelsforespørselsforespørsel, og at en overlapping eksisterer mellom området for den første spredningsgrense og den andre spredningsgrensen, og en markedsspredning bestemmer at markedsprisene eksisterer som ligger innenfor overlappingen, bestemmer et mismatchbeløp i den andre sikkerheten basert på en forskjell mellom kjøpsforholdet og det nevnte salgsforhold som er knyttet til det ene parhandelskrav og kjøpsforholdet og salgsforholdet til den andre parhandelforespørsel beregner et kryssbeløp for den første sikkerheten og den andre sikkerheten velger en kryssepris for den første sikkerheten og den andre sikkerheten som er innenfor nevnte overlapping, bestemmer at nevnte feilparameter er tilgjengelig ved nevnte kryssepris for nevnte andre sikkerhetskampene nevnte andre del av nevnte handel med nevnte første sikkerhet i det ene parhandelskrav og i det minste nevnte første del av handelen av nevnte andre sikkerhet i nevnte ene-par-handelsforespørsel mot nevnte andre parhandelsforespørsel basert på de valgte priser og utfører en transaksjon for nevnte feilparametre av nevnte andre sikkerhet ved nevnte kryssepris for nevnte andre sikkerhet. 38. System ifølge krav 37, karakterisert v e d at Parkryssingsnettverket bestemmer at nevnte feilparametre er tilgjengelig i et eksternt marked ved nevnte kryssingspris for nevnte andre sikkerhet.39. System ifølge krav 37, hvor parkryssingsnettverket bestemmer at nevnte feilparametre er tilgjengelig ved krysseprisen for den andre sikkerheten i sier en ordrebeholdning av en finansinstitusjon. 40. System ifølge krav 24, hvor nevnte eneparhandelskrav og nevnte andre parhandelskrav antyder et antall sprer og hvor parkryssnettverket samsvarer med nevnte andre del av handelen med den første sikkerhet i sa ett par handelsforespørsel og i det minste nevnte første del av handelen med den andre sikkerheten i de ene parhandelskravene t mot det andre par-handelsforespørselen dersom antallet spred er større enn et minimums antall spredninger.41. System ifølge krav 24, hvor nevnte antall parhandelskrav omfatter i det minste noen parhandelskrav som indikerer en preferanse for utførelse via nevnte parkryssing nettverket, hvilket system videre omfatter en porteføljeforvalter i kommunikasjon med nevnte parkryssingsnettverk, idet porteføljestyreren mottar antallet av parhandelskrav og ruting nevnte i det minste noen av nevnte mange handelsforespørsler til nevnte parkryssnettverk i henhold til nevnte preferanse.42 24. System ifølge krav 24, karakterisert ved at systemet videre omfatter en parhandelsmotor for å utføre i det minste noen av nevnte antall parhandelsforespørsler, idet systemet videre omfatter en porteføljeforvalter i kommunikasjon med parhandelsmotor, hvor nevnte flere parhandelskrav omfatter minst noen parhandel forespørsler som indikerer en preferanse for utførelse via paret trading motor, nevnte porteføljeforvalter mottar nevnte antall parhandelsforespørsler og dirigere nevnte i det minste noen av nevnte mange handelsforespørsler til nevnte parhandelsmotor i henhold til nevnte preferanse.43. Fremgangsmåte ifølge krav 24, hvor en klient sender en forespørsel angående en status for paret handelsforespørsel og status for nevnte parhandelsforespørsel blir kontinuerlig oppdatert i realtid.44. Fremgangsmåte ifølge krav 41, hvor preferansen er sendt av en klient elektronisk. 45. Fremgangsmåte ifølge krav 24, hvor en klient mottar en samtidig rapport når paret handler forespørselen er fylt og klienten bekrefter sa parhandel elektronisk.46 Et datamaskinlesbart lagringsmedium som lagrer instruksjoner for å oppfylle en parhandelskode som, når den utføres av en datamaskin, forårsaker at datamaskinen skal motta flere parhandelskrav, omfattende ett par handel forespørsel og en annen par handel forespørsel, hvor hver par handel forespørsel omfatter en forespørsel om å handle en første sikkerhet, en forespørsel om å handle en se cond sikkerhet og en forespørsel om å handle den første sikkerheten og nevnte andre sikkerheten med en minimumspersjonsgrense, og hvor den første sikkerheten og den andre sikkerheten hver har en budpris og en forespørselspris. bestem budbudet spredt i markedet av nevnte første sikkerhet og nevnte andre sikkerhet. determin spør spørsmålet spredes i markedet for den første sikkerheten og nevnte andre sikkerhetsbestemmelser. At minimumspersjonsgrensen for hvert parhandelsforespørsel oppfylles av et utvalg av budbudspredningen og spør spørsmålet om spredning utføre en transaksjon mellom en første del av handelen med nevnte første sikkerhet i nevnte ene-par-handelsforespørsel og minst en ikke-par-handelsforespørsel, forutsatt at minimumspredningsgrensen for det ene parhandelsforespørselen blir oppfylt av rekkevidden av nevnte bud bud spredt og spør spør spørre spredning og match en andre del av nevnte handel av nevnte første sikkerhet i nevnte ene par handel forespørsel og minst en første del av handelen av den andre sikkerheten i det ene par handel req uest mot det andre par-handelsforespørselen, forutsatt at et område av minimumspredningsgrensen for det ene parhandelsforespørselen og den andre parhandelsforespørsel overlapper med nevnte rekkevidde av budbudspredningen og spørsmålet spørs spredningen. KRANS REFERENCE TIL RELATERT ANSØKNING . Denne søknaden hevder fordelen av innleveringsdatoen for den amerikanske foreløpige søknaden Ser nr. 60 334 163, benevnt Metode og System for handelspar av Securities, som ble arkivert 29. november 2001, hvis innhold er innarbeidet som referanse her. Den følgende oppfinnelsen relaterer seg til et system og en metode for handel med verdipapirer, og særlig for et system og en metode for handel med verdipapirer i par. En anerkjent strategi for trading-verdipapirer kalles parhandel. Parhandel er en ikke-rettet investeringsstrategi hvor investor identifiserer to verdipapirer som har lignende egenskaper og verdipapirene handler for tiden til et prisforhold som ligger utenfor deres historiske handelsområde investor utnytter prisforholdet mellom verdipapirene ved å kjøpe den undervurderte sikkerheten mens de selger den overvurderte sikkerheten fordi parhandel er en markedsnøytral strategi. Det er en spesielt ønskelig strategi for å investere i volatile markeder. En kontekst hvor parhandel er nyttig er hvor en investor ønsker å benytte seg av en arbitrage-mulighet som følge av en fusjon mellom to selskaper. For eksempel har Selskap A kunngjort en endelig avtale om å erverve selskap T, og i så fall vil selskapets A-aksjeeiere motta 0 5 aksjer i selskap A-aksje for hver andel av selskapets T-aksje de eier Investoren ønsker å fange spredningen mellom tilbudt vederlag 0 5 A-aksjer og T-aksjekursen For å gjøre dette kjøper investor aksjer i T-aksje og selger aksjer i A-lager. For eksempel , hvis aksje T handler til 28 per aksje og aksje A handler til 60 per aksje, kan investor utføre en handel for 200.000 spredninger ved å kjøpe 200.000 s har T-aksjer og selger 100.000 aksjer i A-aksje Etter at fusjonen finner sted, vil investor dekke den korte posisjonen i A-aksjen med de 100.000 aksjene i A-aksjen som investorene mottar i bytte av de 200.000 aksjene investoren beholdt av aksjen T , ved å utføre parhandel, låser investoren i et 400 000 gevinst forutsatt at fusjonen går gjennom. Prosessen med å utføre et parhandel omfatter således utførelse av individuelle handler rettet mot hvert ben av parhandelskravet. Et eksempel på et system for utførelse av handler for å fylle et parhandelsforespørsel er Quantex-systemet fra ITG på 380 Madison Avenue New York, NY 10017. En utfordring i å implementere et parhandel er å finne en motpart for en bestemt stilling som en investor ønsker å etablere mens minimering av benrisiko. Vanligvis er en stor Parhandel utføres fra markedet som en privat transaksjon som forhandles av en finansinstitusjon som betjener store kunder. For eksempel, hvis en investor ønsker å utføre ap air trade betting at en foreslått fusjon mellom to selskaper vil gå gjennom, ville investor nærme seg en finansinstitusjon som søker en investor som er villig til å satse mot fusjonen. Finansinstitusjonen fungerer da som mellomledd mellom de to investorene der investorene etablerer like og motsatte stillinger i aksjene til de foreslåtte fusjonspartnerne derved fullfører parhandelen Dermed ved å samsvare to parhandelsforespørsler slik at transaksjonene knyttet til hver av parhandelsbenene utføres samtidig, er ingen investor utsatt for beinrisiko som ellers skulle resultere for perioden mellom utførelsen av det første beinet og det andre benet i parhandel. Det er mange ulemper forbundet med den utbredte parhandelspraksis. For det første er parhandel vanligvis begrenset til kunder fra store finansinstitusjoner som har evnen å identifisere egnede motparter for en bestemt parhandel Dette er spesielt tilfellet whe n Parhandelen innebærer en stor mengde aksjer eller illikvide aksjer hvor den eneste måten å utføre handelen og minimere benrisiko er via en av markedstransaksjonen som forhandles av en finansinstitusjon. Også fordi en parhandel vanligvis forhandles av partier med en finansinstitusjon som mellommann, prosessen er ofte sakte og ineffektiv. Videre er parhandel under gjeldende praksis generelt best egnet for store kunder som ønsker å etablere store posisjoner og derved gi finansinstitusjonene det økonomiske incitamentet til å gjennomføre transaksjonen Mindre Klienter må imidlertid stole på markedene for å utføre parhandel, noe som er uegnet for illikvide aksjer og også medfører økt benrisiko. Det er følgelig ønskelig å gi et system og en metode for handel med verdipapirer i par. SAMMENDRAG AV OPPFINNELSEN. Foreliggende oppfinnelse er rettet mot å overvinne ulempene ved den kjente parhandelspraksis. Under foreliggende oppfinnelse a Fremgangsmåten er tilveiebrakt for å oppfylle en parhandelsforespørsel og inkluderer trinnene å motta et antall parhandelskrav som utfører en transaksjon for en første del av en av flere parhandelskrav og samsvarer med en andre del av den ene av flerparten av paret handel forespørsler mot en annen av flere parhandel forespørsler. I en eksempelvis utførelsesform inkluderer fremgangsmåten trinnet å utføre en transaksjon for en første del av en av flere parhandel forespørsler i et eksternt marked. I en annen eksempelvis utførelsesform fremgangsmåten innbefatter trinnet for å utføre en transaksjon for en første del av en av flere parhandelskrav mot ordrebeholdningen. I enda en annen utførelsesform omfatter parhandelskravet en første sikkerhet som har en budpris og en forespørselspris og en andre sikkerheten har en budpris og en spørpris, og metoden inkluderer trinnene for å avgjøre om budprisen på den første sikkerheten og budet pr pr ice of the second security meet a spread limit determining an amount of the second security that can be sold based on a bid size associated with the second security calculating an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusting the equivalent amount of the first security based on adjustment criteria calculating a purchase price for the adjusted equivalent amount of the first security based on the spread limit executing an initiating order to buy the adjusted equivalent amount of the first security at the purchase price and executing a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the method includes the step of executing a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the method includes the steps of determining whether the ask price of the first security and the ask price of the second security and or the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the first security that can be bought based on an offer size associated with the first security calculating an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusting the equivalent amount of the second security based on adjustment criteria calculating a selling price for the adjusted equivalent amount of the second security based on the spread limit executing an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executing a covering order to purchase the amount of the first security. In another exemplary embodiment, the method includes the step of executing a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the adjustment criter ia include a minimum amount and a maximum amount. In still yet another exemplary embodiment, the method includes the step of rounding the initiating order to a round lot size. In an exemplary embodiment, the method includes the step of executing a first portion of one of the plurality of pair trade requests in a plurality of tranches. In another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of said plurality of trade requests has a second spread limit and wherein the method includes the steps of determining that a range of the first spread limit and the second spread limit overlaps with a market spread setting a spread level calculating prices for the first security and the second security that are within the market spread and based on the spread level and matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In yet another exemplary embodiment, the method includes the steps of calculating a mean between the first spread limit and the second spread limit and setting the spread level as the mean if the mean is within the market spread. In still yet another exemplary embodiment, the method includes the step of identifying a spread amount that is closest to the mean and within the market spread and setting the spread level as the spread amount if the mean is not within the market spread. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and the method includes the steps of determining that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determining that market prices exist that are within the overlap determining a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculating a cross amount for the first security and the second security selecting a crossing price for the first security and the second security that is within the overlap determining that the mismatch amount is available at the crossing price for the second security matching the second portio n of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executing a transaction for the mismatch amount of the second security at the crossing price for the second security. In another exemplary embodiment, the method includes the step of determining that the mismatch amount is available in an external market at the crossing price for the second security. In yet another exemplary embodiment, the method is performed by a financial institution having order inventory and includes the step of determining that the mismatch amount is available in the order inventory at the crossing price for the second security. In still yet another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and the method includes the step of matching a second portion of the one of the plurality of pair trade requests against anot her of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In an exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of executing a transaction for a first portion of one of the plurality of pair trade requests, described above. In another exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests, described above. Under the present invention, a method for fulfilling a pair trade request is provided and includes the steps of receiving a plurality of pair trade requests and matching at least a portion of one of the plurality of pair trade requests against another of the plurality of pair trade requests. Under the pr esent invention, a system for fulfilling a pair trade request is provided, the system receiving a plurality of pair trade requests and includes a pair trading engine for executing a transaction for a first portion of one of the plurality of pair trade requests The system also includes a pair crossing network for matching a second portion of said one of the plurality of pair trade requests against another of the plurality of pair trade requests. In an exemplary embodiment, the system includes a link to external markets and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests in the external markets. In another exemplary embodiment, the system includes a financial institution having an order inventory and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request in cludes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and wherein the pair trading engine determines whether the bid price of the first security and the bid price of the second security meet a spread limit determines an amount of the second security that can be sold based on a bid size associated with the second security calculates an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusts the equivalent amount of the first security based on adjustment criteria calculates a purchase price for the adjusted equivalent amount of the first security based on the spread limit executes an initiating order to buy said adjusted equivalent amount of the first security at the purchase price and executes a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the pair trading engine executes a covering order to sell th e amount of the second security at the bid price of the second security. In an exemplary embodiment, the pair trading engine determines whether the ask price of the first security and the ask price of the second security meet a spread limit determines an amount of the first security that can be bought based on an offer size associated with the first security calculates an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusts said equivalent amount of the second security based on adjustment criteria calculates a selling price for the adjusted equivalent amount of the second security based on the spread limit executes an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executes a covering order to purchase the amount of the first security. In another exemplary embodiment, the pair trading engine executes a covering order to purchase the amount of the first securi ty at the ask price of the first security. In yet another exemplary embodiment, the pair trading engine rounds the initiating order to a round lot size. In still yet another exemplary embodiment, the pair trading engine executes a first portion of one of the plurality of pair trade requests in a plurality of tranches. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of the plurality of trade requests has a second spread limit and wherein the pair crossing network determines that a range of the first spread limit and the second spread limit overlaps with a market spread sets a spread level calculates prices for the first security and the second security that are within the market spread and based on the spread level and matches the second portion of said one of the pluralit y of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In another exemplary embodiment, the pair crossing network calculates a mean between the first spread limit and the second spread limit and sets the spread level as the mean if the mean is within the market spread. In yet another exemplary embodiment, the pair crossing network identifies a spread amount that is closest to the mean and within the market spread and sets the spread level as the spread amount if the mean is not within the market spread. In still yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and wherein the pair crossing net work determines that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determines that market prices exist that are within the overlap determines a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculates a cross amount for the first security and the second security selects a crossing price for the first security and the second security that is within said overlap determines that the mismatch amount is available at the crossing price for the second security matches the second portion of the one of the plurality of pair trade requests aga inst another of the plurality of pair trade requests based on the calculated prices and executes a transaction for the mismatch amount of the second security at the crossing price for the second security. In an exemplary embodiment, the pair crossing network determines that the mismatch amount is available in an external market at the crossing price for the second security. In another exemplary embodiment, the pair crossing network determines that the mismatch amount is available in the order inventory at the crossing price for the second security. In yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and wherein the pair crossing network matches a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In still yet another exemplary embodim ent, the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via said pair crossing network, and the system further includes a portfolio manager in communications with the pair crossing network, the portfolio manager receiving the plurality of pair trade requests and routing the at least some pair trade requests to the pair crossing network according to the preference. In an exemplary embodiment, the system includes a pair trading engine for executing at least some of the plurality of pair trade requests, further includes a portfolio manager in communications with the pair trading engine and wherein the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via the pair trading engine, the portfolio manager receiving the plurality of pair trade requests and routing the at least some of the plurality of trade requests to the pair trading engine according to the preferenc e. Under the present invention, a system for fulfilling a pair trade request is provided, wherein the system receives a plurality of pair trade requests and includes a pair crossing network for matching at least one of the plurality of pair trade requests against another of the plurality of pair trade requests. Accordingly, a method and a system are provided for trading pair securities. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims Other features and advantages of the invention will be apparent from the description, the drawings and the claims. DESCRIPTION OF THE DRAWINGS. For a fuller understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings, in which. FIG 1 is a block diagram of a system for trading securities in pairs accordi ng to the present invention. FIG 2 is a flowchart of the steps a pair trading engine included in the system of FIG 1 applies to fill a pair trade request. FIG 3 is a flowchart of the steps a pair crossing network included in the system of FIG 1 applies to fill a pair trade request. FIG 4 is a flowchart of a process by which the pair crossing network of the system of FIG 1 fills imperfectly matched orders and. FIG 5 is a graph for identifying the market prices for two securities that meet the required spread limits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS. Referring now to FIG 1 there is shown a block diagram of a system 1 for trading securities in pairs according to the present invention System 1 receives pair trade requests from clients operating client access devices 7 and attempts to fill the pair trade requests according to the parameters associated with the particular pair trade request System 1 includes two different subsystems for filling pair trade requests a pair trading e ngine 3 and a pair crossing network 5 As will be described below, pair trading engine 3 receives a pair trade request and attempts to fill in whole or in part the trade request by executing the appropriate trades in an external market 13 that may include, by way of non-limiting example, the New York Stock Exchange, the NASDAQ or any other financial market Pair trading engine 3 may also fill in whole or in part a pair trade request by executing a transaction against order inventory 11 of non-pair trade requests controlled by the financial institution that is operating system 1 In addition, pair trading engine may also fill in whole or in part a pair trade request by forwarding the trade request to pair crossing network 5 for matching with other pair trade requests. Likewise, pair crossing network 5 receives a pair trade request and fulfills in whole or in part the request by matching it against another pair trade request received by pair crossing network 5 by matching the request against inventory 11 controlled by the financial institution and or by forwarding the trade request to pair trading engine 3 for execution in external markets 13.System 1 also includes a portfolio manager 9 that may be, for example, a software program executing on a computer system that receives the pair trade requests from client access device 7 and presents the trade request to either pair trading engine 3 pair crossing network 5 or both, depending on the trade parameters set by the client Also, the client may query portfolio manager 9 regarding the status of any pair trade request the client has presented to system 1.In operation, system 1 may fulfill a pair trade request either using pair trading engine 3 or pair crossing network 5 or a combination of the two For example, a pair trade request received by system 1 may be completely filled by pair trading engine 3 as follows. Assume a case where XYZ is taking over ABC and is offering 0 575 shares of XYZ for each ABC share and investor Arb wa nts to invest in the price difference between ABC stock and XYZ stock To take advantage of the price difference, Arb wants to lock in the difference between the value offered 0 575 XYZ stock and the value of ABC stock by buying ABC stock and selling XYZ stock subject to the condition that ABC 0 575 XYZ 1 19 i e Arb desires to capture a 1 19 difference between XYZ s takeover offer and ABC s share price. In order to fill this pair trade, Arb presents a pair trade request to portfolio manager 9 using client access device 7 The pair trade request typically includes a number of parameters that define the pair trade and that also may be used by portfolio manager 9 in determining how the pair trade request is to be filled Arb typically indicates in the trade request the number of spreads the Arb desires to invest in and also provides a minimum and maximum share amount that he is willing to trade per tranche. For example, Arb may indicate a desire to invest in 100,000 spreads and may only wish t o trade the spread 3,000-8,000 shares at a time Arb generally sets this tranche size range based on the liquidity and volatility of ABC stock and XYZ stock Arb may set a larger minimum tranche size if ABC stock and XYZ stock are fairly liquid stocks because higher liquidity increases the likelihood that a larger tranche size will be executed Arb may set a lower maximum tranche size if XYZ stock and ABC stock are volatile stocks so as to limit the leg risk associated with executing a pair trade. Yet another pair trade parameter Arb provides is the spread limit in the above case 1 19 which is the amount Arb desires to capture in the trade Arb does not have to provide, however, the discrete prices at which trades for ABC and XYZ stock are to be executed as these prices are calculated by pair trading engine 3 and or pair crossing network 5 , as will be described below. Referring now to FIG 2 there is shown a flowchart describing the steps pair trading engine 3 applies to fill a pair trade re quest The flowchart in FIG 2 is based on the above example and the market data listed in Table 1 below. Initially, in Step 201 pair trading engine 3 determines whether the bid bid prices or ask ask prices of ABC and XYZ stock, respectively, meet the spread limit requirement of the particular pair trade request In this case the bid bid spread is 1 4375 122 50 0 575 69 and the ask ask spread is 1 1969 122 625 0 575 69 3125 so that each spread is less than the spread limit of 1 19, as is required for this particular trade Once it is determined that either the bid bid spread or the ask ask spread meets the spread limit, then in Step 202 it is determined as is indicated in Table 1 how much XYZ stock can be sold at the bid and how much ABC stock can be bought at the ask In an exemplary embodiment, the client may specify whether the bid bid spread, the ask ask spread or either the bid bid or the ask ask spread must exceed the indicated spread limit for a transaction to proceed If neither the b id bid spread nor the ask ask spread meets the spread limit, the process waits a period of time for example 0 10 seconds and returns to Step 201 to again test whether the bid bid spread or the ask ask spread meets the spread limit. Next, in step 203 an equivalent amount of stock that can be sent into the market i e bought sold in the market is calculated for a spread based on the bid bid price spread and or the ask ask price spread that meets the spread limit In this example, if a maximum of 10,000 shares of XYZ stock can be sold into the market i e the XYZ bid size then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 17,391 10,000 0 575 shares of ABC stock are to be bought in order to execute a balanced pair trade Likewise, if a maximum of 1,500 shares of ABC stock can be bought in the market i e the ABC ask size , then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 863 1500 0 575 shares of XYZ stock are to be sold in order to execute a balanced pair trade. Next, in Step 204 the pair trade share amounts calculated in Step 203 are adjusted to conform to the wave maximum and minimum parameters i e the maximum minimum tranche size included in the pair trade request as well as market round lot limits In the above example, the amount of ABC shares to be bought that was calculated based on the XYZ bid size i e 17,391 is first rounded to an even lot size i e 17,400 and then reduced to the maximum tranche size of 8000 Also, the amount of XYZ shares to be offered that was calculated based on the ABC ask size i e 863 is first rounded to an even lot size i e 900 and then increased to 1,700 shares to meet the minimum tranche size of 3000 3000 0 575 1777 In an exemplary embodiment the minimum and maximum tranche size is scaled by the particular ratio for example, in the above case, the tranche sizes for XYZ stock is scaled by 0 575 In another embodiment, the maximum minimum tranche size is used for each security in the pair trade request without scaling In yet another exemplary embodiment, the pair trade request includes a separate maximum minimum tranche for each security. Once the share amounts for the pair trade are calculated, in Step 205 the share prices that are needed to meet the spread limit of the pair trade request are calculated For example, for a pair trade based on the bid bid price spread, in order to meet the spread limit of 1 19 credit, the price at which ABC stock is to be bid should be no greater than 69 2475 122 50 0 575 1 19 a share Likewise, for a pair trade based on the ask ask price spread, in order to meet the spread limit, the price at which XYZ stock is to be offered should be greater than or equal to 122 6130 69 3125 1 19 0 575 a share. Next, once the pair trade share amounts and share prices have been calculated, in Step 206 pair trading engine 3 sends initiating orders to external markets 13 in order to fill the pair trade request The initiating orders may include an initiating order for executing a pair trade based on the bid bid spread in this case a bid for 8,000 shares of ABC stock at 69 2475 and or an initiating order for executing a pair trade based on the ask ask spread in this case an offer of 1,700 shares of XYZ stock at 122 6130.Finally, as the initiating orders sent to external markets 13 in Step 207 get filled, pair trading engine 3 automatically sends into the market the covering side of the pair trade So, for example, as the initiating order of buying 8,000 shares of ABC stock at 69 2475 gets filled, pair trading engine 3 sends an order to external markets 13 to sell 4,600 8,000 0 575 shares of XYZ stock at 122 50.In an exemplary embodiment, the client s pair trade request includes threshold amounts that indicate the amount of variance in stock price and or share amount the client is willing to absorb For example, if in the process of covering the initiating order the price of XYZ stock dips to 122 49 in which case the spread limit of the pair trade would drop to 1 18 , then pair trading engine 3 would still sell XYZ stock at the price of 122 49 if the 0 01 difference was within the threshold amount included in the pair trade request Similarly, the pair trade request may include threshold amounts for any other pair trade parameter, including by way of non-limiting example, the number of spreads to be purchased and the tranche sizes If, however, a particular threshold amount indicated by the client is exceeded for any given pair trade parameter, then pair trading engine 3 would attempt to cancel the initiating order and or the covering order that may be possible if the orders have not yet reached the market or have not yet been filled In such a case, pair trading engine 3 would then repeat the above analysis for determining suitable initiating and cover orders. To fill a pair trade request, pair trading engine 3 executes trades utilizing the method described above Typically, pair trading engine 3 tranches a pair trade request and trades piece-meal in external markets 13 In certain cases, however, it may be difficult to fill a trade request by executing several transactions in external markets 13 either because the pair trade request is for a very large number of spreads or includes stocks that are illiquid in which cases pair trading engine 3 may be ineffective in filling the pair trade request Also, in certain situations, a client wishing to remain anonymous may indicate in the pair trade request a preference that no orders be sent to external markets 13 In these circumstances, portfolio manager 9 may route the particular pair trade request to pair crossing network 5.Referring now to FIG 3 there is shown a flowchart illustrating the steps pair crossing network 5 applies to fill a pair trade request The flowchart in FIG 3 is based on the above example and the market data listed in Table 2 below. Spread Limit as defined by 0 575 XYZ - ABC. Continuing the previous example, assume the pair trade request issued by Arb for 100,000 spreads was half-filled by pair trading engine 3 Also, assume that system 1 receives a pair trade request from Antiarb that indicates a desire to sell 30,000 shares of ABC and buy 17,200 shares a ratio of 1 0 575 and also indicates a spread limit of 1 30 i e ABC 0 575XYZ 1 30 In this case Arb and Antiarb s orders are complimentary in the primary order elements securities, ratios and buy versus sell Also, Antiarb is willing to pay 0 11 per spread more than Arb is demanding from the marketplace Based on these parameters, there is an opportunity for Arb s and Antiarb s trade requests to be filled via pair crossing network 5.If Antiarb s pair trade request was marked for trading by pair trading engine 3 then portfolio manager 9 sends Antiarb s order to pair trading engine 3 for execution Pair trading engine 3 then sends the parameters of Antiarb s trade reques t, as well as all orders waiting for execution in pair trading engine 3 to pair crossing network 5 Pair crossing network 5 will recognize as described above that there is a crossing opportunity between Arb s order and Antiarb s order In this case, pair crossing network 5 then directs pair trading engine 3 to suspend the execution of Antiarb s order in the amount that can be crossed by pair crossing network 5 30,000 spreads in this case In addition, pair trading engine 3 routes a cross amount of 30,000 spreads from Arb s order to pair crossing network 5 for crossing against Antiarb s order At this point, the pair crossing network 5 crosses the Antiarb order against a portion of Arb s order, as follows. Assume the prevailing market conditions at the time of the cross are as shown in Table 3 Furthermore, Table 3 indicates the XYZ Ratio-Adjusted Value for both the bid and ask prices based on the conversion ratio of 1 0 575 Based on the XYZ Ratio-Adjusted Values, a Bid Ask Spread Range i e t he spread provided for a cross between the bid price of ABC stock and the XYZ Ratio-Adjusted ask price of 1 3863 is calculated and an Ask Bid Spread Range i e the spread provided for a cross between the ask price of ABC stock and the XYZ Ratio-Adjusted bid price of 1 05 is calculated. To perform the cross, in Step 301 pair crossing network 5 first determines whether the range of spread limits associated with Arb s and Antiarb s trade requests i e 1 30- 1 19 coincides with the range of the prevailing market spread 1 3863- 1 05 In this example, the range of spread limits does coincide with the prevailing market spread because at least a portion of the spread limit range overlaps with a portion of the market spread Thus, a cross can occur. Next, in Step 302 pair crossing network 5 calculates the mean of Arb s and Antiarb s spread order limit which is 1 30 1 19 2 1 245 and determines whether the mean is within the range of the market spread i e 1 3863- 1 05 If it is, then in Step 303 pair cr ossing network 5 calculates the prices at which to cross The prices must be within the current markets for ABC stock and XYZ stock, and satisfy market uptick requirements for short sales , and provide a spread that is equal to the spread level calculated above For example, with the inside market for ABC stock at 70 00-70 25 and the inside market for XYZ stock at 124 00-124 15, a cross price of 70 11 for ABC stock and 124 096 for XYZ stock provides the spread of 1 2452 thereby meeting the requirement of both Arb s and Antiarb s trade request Finally, in Step 304 pair crossing network 5 crosses 30,000 shares of ABC stock at 70 11 with Arb buying and Antiarb selling and 17,200 shares of XYZ at 124 096 with Arb selling and Antiarb buying. If it is determined in Step 302 that the mean of Arb s and Antiarb s spread order limits does not fall within the range of the market spread, then in Step 305 the spread closest to the mean of the two spread limits that is also within the market spread is calculated For example, if the market spread is 1 3863- 1 28, then the mean of the two spread limits 1 245 is not within the market spread In such a case, 1 28 is selected as the spread level that is closest to the mean and within the market spread In an exemplary embodiment, the spread level at which Arb and Antiarb cross can be determined in any other suitable manner as long as the spread level is within the market spread and within the range of spread limits indicated in the pair trade requests. Once the spread level is determined, the method proceeds to Step 303 in which pair crossing network 5 calculates prices to cross at that are within the current markets for ABC stock and XYZ stock and that meet the calculated spread level In the case where the calculated spread level is 1 28, the cross will occur at a price of 70 08 for ABC stock and 124 1043 for XYZ stock Finally, the method proceeds to Step 304 in which pair crossing network 5 performs the cross between Arb and Antiarb. Once a pair trade request is filled or partially filled , the transaction details are reported to portfolio manager 9 and made available to the client operating client access device 7.In the previous example, pair crossing network 5 crosses orders in which both Arb and Antiarb desire to trade the same pair of securities in the same ratio In an exemplary embodiment, pair crossing network 5 executes a cross between two pair trade requests that are not perfectly matched. For example, assume that pair crossing network 5 receives the pair trade requests as shown in Table 4 Note that these two pair trade requests are imperfectly matched because each trade request uses a different ratio between ABC and XYZ stock. Arb s Spread Limit is defined by 0 575 XYZ - ABC. Antiarb s Spread Limit is defined by 0 6 XYZ - ABC. Also, assume the market in ABC and XYZ stocks at the time the pair trade requests are received by pair crossing network 5 is as described in Table 5 below. Arb s XYZ Ratio-Adjusted Value. Arb s Dollar Range. AntiArb s XYZ Ratio-Adjusted Value. AntiArb s Dollar Range. Referring now to FIG 4 there is shown a flowchart illustrating a process by which pair crossing network 5 fills these imperfectly matched order First, in Step 401 pair crossing network 5 determines whether Arb s buy security equals Antiarb s sell security and whether Arb s sell security equals Antiarb s buy security If both conditions are not met, then a cross between the two orders cannot occur If the two conditions are met, then in Step 402 it is determined whether Arb s buy ratio equals Antiarb s sell ratio and whether Arb s sell ratio equals Antiarb s buy ratio If these ratios are the same, then pair crossing network 5 procee ds to cross the two orders as described in the example above Note that for a cross to occur at this stage does not require the ratios themselves to match but rather that the ratios of the ratios match for e g a ratio of 2 3 matches a ratio of 0 667 1.If, however, the two ratios are not equal as in this case where Arb s sell ratio does not equal Antiarb s buy ratio , then in Step 403 pair crossing network determines whether there is an overlap between Arb s and Antiarb s spread limit that also falls within the bid ask market for ABC and XYZ stock To make such a determination, pair crossing network 5 calculates whether there are market prices for both ABC and XYZ stock that satisfy the following inequalities L 1 Ratio A ABC Ratio B XYZ and 1 L 2 Ratio C ABC Ratio D XYZ 2 Where L1 is Arb s spread limit of 1 19 credit, L2 is Antiarb s spread limit of 4 40 debit, RatioA is Arb s buy ratio of 1 1, RatioB is Arb s sell ratio of 1 0 575, RatioC is Antiarb s sell ratio of 1 1 and RatioD is Anti arb s buy ratio of 1 0 6.Referring now to FIG 5 there is shown a graph 51 that depicts market prices for ABC and XYZ stock that meet the spread limits of Arb and Antiarb In graph 51 the x-axis represents the prices for XYZ stock while the y-axis represents the prices for ABC stock Graph 51 includes a shaded area 53 that is the universe of market prices for ABC and XYZ stock that could satisfy the spread trade involving those stocks Also included in graph 53 is a spreadlimit line L1 inequality 1 , above that represents the spread limit associated with Arb and a spread limit line L2 inequality 2 , above that represents the spread limit associated with Antiarb Thus, the solution set of market prices that satisfies inequalities 1 and 2 is the portion of dark shared area 53 that falls between spread limit line L1 and spread limit line L2 In this example, a cross at a share price for ABC of 70 14 and a share price of 124 15 for XYZ stock meets the investor s spread limits and falls within th e market prices for ABC and XYZ stock. If it is determined that no share prices for both ABC and XYZ stock satisfy Arb s and Antiarb s spread limits, then no cross can occur If such share prices do exist, then in Step 404 it is determined which of the investors desires to transact in fewer shares of ABC stock and a mismatch in share amounts caused by the differing ratios is determined In our example, Antiarb desires to sell fewer ABC shares than Arb desires to buy 30,000 vs 50,000 Then, in Step 405 pair crossing network 5 determines the number of XYZ shares that can be crossed between Arb and Antiarb based on the maximum amount of ABC shares that can be crossed 30,000 in this example Based on the Antiarb ABC order quantity of 30,000 shares, the maximum number of XYZ shares that Arb will cross with Antiarb is.30 000 Arb XYZ Ratio Arb ABC Ratio 30 000 0 575 1 17 300 17 250 rounded to an even lotsize. While the maximum quantity of XYZ shares that Arb will cross is 17,300, Antiarb s trade re quest indicates a desire to cross 18,000 shares To overcome this imbalance, in Step 406 pair crossing network 5 is in communications with external markets 13 for determining whether the excess 700 XYZ shares needed to satisfy Antiarb s trade request can be transacted for in external markets 13 In an exemplary embodiment, pair crossing network 5 makes this determination by issuing a query to pair trading engine 3 as to whether 700 shares of XYZ stock can be bought in external markets 13 Because, as indicated in Table 5, 3,000 shares of XYZ stock are offered at 124 15, pair trading engine 3 responds to pair crossing network 5 that the 700 shares needed to balance the cross between Arb and Antiarb are available from external markets 13 at 124 15.Next, in Step 407 pair crossing network calculates the cross prices that are necessary such that Arb and Antiarb achieve their respective spread limits while also incorporating the excess 700 shares of XYZ stock that must be purchased from externa l markets 13 at 124 15 to satisfy Antiarb s trade request An example of such cross prices that meet these criteria is a price of 70 14 for ABC stock and a price of 124 15 for XYZ stock. Once the cross prices are calculated, in Step 408 pair crossing network 5 crosses 30,000 shares of ABC stock and 17,300 shares of XYZ stock between Arb and Antiarb and also buys 700 shares of XYZ stock at 124 15 in external markets 13 on behalf of Antiarb Thus, both Arb and Antiarb s pair trade requests are satisfied. Alternatively, the entire 18,000 shares of XYZ stock may be crossed thereby fully satisfying Antiarb s trade request In such a case, the ratio mismatch is addressed by Arb purchasing an additional 1200 700 0 575 rounded to a lotsize shares of ABC stock from external market 13 or from firm inventory 11.Once the trade is completed, the details of the transaction are provided to portfolio manager 9 to report the transaction details to the investors. In an exemplary embodiment, a pair order or po rtion thereof may be filled against an internal inventory 11 of trade requests maintained by the financial institution operating system 1 For example, in the previous example in which an excess of 700 shares of XYZ stock needs to be purchased in order for a match i e cross between Arb and Antiarb s trade requests to occur, instead of determining whether the 700 shares are available in external markets 3 pair crossing network 5 examines firm inventory 11 to determine whether the shares are available at the required price Likewise, in cases where pair trading engine 3 desires to execute a pair trade based on orders to be sent to external markets 13 pair trading engine 3 may first determine whether the order can be filled, in whole or in part, using trade requests pending in firm inventory 11 Generally, the advantages of filling an order using pending trade requests in firm inventory 11 is that execution is faster, transaction costs are lower and leg risk is minimized. In another exemplary embodiment, a client s pair trade request may also include a minimum number of spreads that can be traded in pair crossing network 5 Also, pair crossing network 5 may be designed to require a minimum share amount for a cross to occur A minimum number of spreads that can be traded may be provided in order to reduce the distractions and booking costs associated with numerous smaller trades that may exceed the benefits of a de minimis fill. In another exemplary embodiment, portfolio manager 9 publishes the inside cross market for any pair that a client has selected for crossing in pair crossing network 5 In still another exemplary embodiment, the client has the option for each pair trade selected for crossing in pair crossing network 5 to designate that the order should be reflected in the published inside cross market This inside cross market consists of the tightest spread bid and offer and corresponding bid size and offer size from all client pair orders pending in pair crossing networ k 5 In this way, a client can assess the likelihood and timing of a pair trade request being filled by pair crossing network 5 Also, by publishing the client s spread interest, others seeking liquidity can trade at the client s level. In an exemplary embodiment, the client can designate each pair order designated for pair trading engine 3 and or pair crossing network 5 for Broker Negotiation If Broker Negotiation is designated, the client s broker-dealer sales representative is notified of the client s spread order thereby prompting the broker-dealer to solicit a complementary, agency order from another client The client may also designate each pair order for Broker Facilitation in which case the client allows the broker-dealer to act principally to fill the client s order. In summary, the advantages to a client of using pair trading engine 3 is that pair trading engine 3 allows the client to trade a spread order while limiting leg risk or the risk of missing a targeted spread level This is accomplished by breaking the total order into tranches of sizes proportionate to the market, subject to user minimums and maximums, that can be traded in external markets 13 or against firm inventory 11 Orders executed via pair trading engine 3 however, are typically of a lower traded volume because trading is constrained to the liquidity available in the market In contrast, trades executed via pair crossing network 5 are not constrained by market liquidity and do not have to be tranched to minimize leg risk In particular, the benefits of filling a pair trade request via pair crossing network 5 are as follows. Elimination of Leg Risk Pair crossing network 5 potentially provides a deeper well of liquidity because the trades are brokered, as a spread, directly between spread investors via a central clearing facility Moreover, the introduction and use of a pair trading facility eliminates the leg risk described above without a sacrifice of liquidity. Large Transactions Only Certain larg e investors may prefer to use pair crossing network 5 rather than pair trading engine 3 to avoid having a trade request broken up into numerous small executions For example, sudden, brief moves in one of the two stocks included in the pair trade request may cause pair trading engine 3 to issue numerous small executions to fill the request While a small investor may welcome capturing these small opportunities, a large investor may find such small executions to be more of a nuisance than a service. Price Setting versus Price Taking Large investors seeking liquidity may prefer to set their price via the pair crossing network 5 Also, other spread investors looking for liquidity can use pair crossing network 5 to monitor and trade with the large investor at the large investor s level While client orders directed to pair trading engine 3 can designate a spread limit, such orders are essentially price-takers as the market reaches the desired level, the orders are executed Moreover, the pair tr ading engine tranching mechanism creates relatively small orders, allowing institutional flows to move the individual stocks As a result, the small, tranched orders generated by pair trading engine 3 can become overpowered by single-name institutional flows In addition, orders designated solely for pair trading engine 3 and not for pair crossing network 5 are not published to a central quote facility such as by portfolio manager 9 thereby preventing other spread traders from knowing the size and limit of a pair trading engine order. Illiquid Stocks vs Liquid Stocks Spreads that include one or two illiquid stocks are difficult to fill using pair trading engine 3 alone Because illiquid stocks often demonstrate small bid and ask sizes and wide bid-ask spreads, pair trading engine 3 will typically only issue market orders having small quantities subject to user minimums and maximums that presents the client with greater leg risk from mid-trade changes in the bid-ask prices In contrast, orde rs routed to price crossing network 5 are not confined by liquidity in the market place thereby allowing large crosses between spread traders in illiquid spreads. Accordingly, a system and method for trading pair securities is provided in which the client receives the benefits of having a pair order filled by either pair trading engine 3 pair crossing network 5 or a combination of both. A number of embodiments of the present invention have been described Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention Based on the above description, it will be obvious to one of ordinary skill to implement the system and methods of the present invention in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device Each computer program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired and in any case, the language may be a compiled or interpreted language Suitable processors include, by way of example, both general and special purpose microprocessors Furthermore, alternate embodiments of the invention that implement the system in hardware, firmware or a combination of both hardware and software, as well as distributing modules and or data in a different fashion will be apparent to those skilled in the art and are also within the scope of the invention In addition, it will be obvious to one of ordinary skill to use a conventional database management system such as, by way of non-limiting example, Sybase, Oracle and DB2, as a platform for implementing the present invention Also, network access devices can comprise a personal computer executing an operating system such as Microsoft Windows , U nix , or Apple Mac OS , as well as software applications, such as a JAVA program or a web browser Access devices can also be a terminal device, a palm-type computer, mobile WEB access device or other device that can adhere to a point-to-point or network communication protocol such as the Internet protocol Computers and network access devices can include a processor, RAM and or ROM memory, a display capability, an input device and hard disk or other relatively permanent storage Accordingly, other embodiments are within the scope of the following claims. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process, in a described product, and in the construction set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shown in the accompanying drawing shall be i nterpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween. A method is provided for fulfilling a pair trade request and includes the steps of receiving a plurality of pair trade requests executing a transaction for a first portion of one of the plurality of pair trade requests and matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests. 20.The invention claimed is.1 A computer-implemented method for fulfilling a pair trade request, said pair trade request performed by a financial institution having an order inventory, the method comprising the steps of. receiving a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determining the bid bid spread in the market of said first security and said second security. determining the ask ask spread in the market of said first security and said second security. determining that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said first security in said one pair trade request and at least one non-pair trade request in an external market, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. executing a transaction between one of a second portion of said trade of said first security in said one pair trade request or a first portion of the trade of said second security in said one pair trade request, and at least one non-pair trade request in said order inventory, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. wherein at least one of said steps is implemented with a computer.2 The method of claim 1 further comprising. executing a transaction between a portion of the trade of said second security in said one pair trade request and at least another non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. and wherein the steps of executing said first portion of the trade of said first security in said one pair trade request and executing said portion of the trade of said second security in said one pair trade request include the steps of. determining whether the bid price of the first security and the bid price of the second security meet a spread limit. determining an amount of the second security that can be sold based on a bid size associated with the second security. calculating an equivalent amount of said first security that can be bought based on the amount of said second security that can be sold. adjusting said equivalent amount of said first security based on adjustment criteria. calculating a purchase price for said adjusted equivalent amount of said first security based on the spread limit. executing an initiating order to buy said adjusted equivalent amount of said first security at said purchase price a nd. executing a covering order to sell said amount of the second security.3 The method of claim 2 wherein the step of executing a covering order to sell includes the step of. executing a covering order to sell said amount of the second security at the bid price of the second security.4 The method of claim 2 further comprising the steps of. determining whether the ask price of the first security and the ask price of the second security meet a spread limit. determining an amount of the first security that can be bought based on an offer size associated with the first security. calculating an equivalent amount of said second security that can be sold based on the amount of the second security that can be bought. adjusting said equivalent amount of said second security based on adjustment criteria. calculating a selling price for said adjusted equivalent amount of said second security based on the spread limit. executing an initiating order to sell said adjusted equivalent amount of said second se curity at said selling price and. executing a covering order to purchase said amount of the first security.5 The method of claim 4 wherein the step of executing a covering order to purchase includes the step of. executing a covering order to purchase said amount of the first security at the ask price of the first security.6 The method of claim 4 wherein said adjustment criteria include a minimum amount and a maximum amount.7 The method of claim 4 wherein the step of executing an initiating order includes the step of. rounding said initiating order to a round lot size.8 The method of claim 1 further comprising. executing a transaction between a portion of the trade of said second security in said one pair trade request and at least another non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. and wherein the steps of executing said first portion of the trade of said first security in said one pair trade request and executing said portion of the trade of said second security in said one pair trade request includes the steps of. determining whether the ask price of the first security and the ask price of the second security meet a spread limit. determining an amount of the second security that can be bought based on an ask size associated with the second security. calculating an equivalent amount of said first security that can be sold based on the amount of the second security that can be bought. adjusting said equivalent amount of said first security based on adjustment criteria. calculating a selling price for said adjusted equivalent amount of said first security based on the spread limit. executing an initiating order to sell said adjusted equivalent amount of said first security at said selling price and. executing a covering order to purchase said amount of said second security.9 The method of claim 1 wherein at least one of the executing steps include the step of. ex ecuting at least a portion of the trade of said first security or said second security in said one pair trade request in a plurality of tranches.10 The method of claim 1 wherein said plurality of pair trade requests comprises another pair trade request, wherein said another pair trade request comprises a request to trade said first security, a request to trade said second security and wherein said one pair trade request has a first spread limit and said another pair trade request has a second spread limit and wherein said method further comprises the steps of. determining that the minimum spread limit of said another pair trade request is met by said range of said bid bid spread and said ask ask spread and. matching another portion of said trade of said first security in said one pair trade request and at least another portion of said trade of said second security in said one pair trade request against said another pair trade request, provided that a range of the minimum spread limit of said one pair trade request and said another pair trade request overlaps with said range of said bid bid spread and said ask ask spread.11 The method of claim 10 wherein said matching step further includes the steps of. determining that a range of said first spread limit and said second spread limit overlaps with a market spread. setting a spread level. calculating prices for the first security and the second security that are within the market spread and based on said spread level and. matching said another portion of said trade of said first security in said one pair trade request and at least said another portion of the trade of said second security in said one pair trade request against said another pair trade request based on said calculated prices.12 The method of claim 11 wherein the step of setting a spread level includes the steps of. calculating a mean between said first spread limit and said second spread limit and. setting said spread level as said mean if said mean is within sai d market spread.13 The method of claim 12 further including the step of. identifying a spread amount that is closest to said mean and within said market spread and. setting said spread level as said spread amount if said mean is not within said market spread.14 A computer-implemented method for fulfilling a pair trade request, comprising the steps of. receiving a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determining the bid bid spread in the market of said first security and said second security. determining the ask ask spread in the market of said first security and said second security. determining that the minimum spread limit of said pair trade re quest is met by a range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said first security in said one pair trade request and at least a first non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. executing a transaction between a first portion of the trade of said second security in said one pair trade request and at least a second non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. repeating the executing steps until the pair trade request is fulfilled. wherein at least one of said steps is implemented with a computer.15 The method of claim 14 wherein at least one of the repeated steps includes the step of. executing a transaction for a portion of the trade of said first security in said one pair trade re quest in an external market.16 The method of claim 14 wherein at least one of the repeated executing steps is performed by a financial institution having an order inventory and at least said one of said repeated steps includes the step of. executing a transaction for a portion of the trade of said first security in said one pair trade request against said order inventory.17 The method of claim 14 wherein said plurality of pair trade requests comprises another pair trade request, wherein said another pair trade request comprises a request to trade said first security, a request to trade said second security and a request said first security and said second security with a second minimum spread limit, the method further comprising the steps of. determining that the minimum spread limit of said another pair trade request is met by said range of said bid bid spread and said ask ask spread and. matching a second portion of said trade of said first security in said one pair trade request and at least a first portion of the trade of said second security in said one pair trade request against said another pair trade request, provided that a range of the minimum spread limit of said one pair trade request and said another pair trade request overlaps with said range of said bid bid spread and said ask ask spread.18 A computer readable storage medium storing instructions for fulfilling a pair trade request that, when executed by a computer, cause the computer to. receive a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determine the bid bid spread in the market of said first security and said second security. determine the ask ask spread in the ma rket of said first security and said second security. determine that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said first security in said one pair trade request and at least one non-pair trade request in an external market, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. execute a transaction between one of a second portion of said trade of said first security in said one pair trade request or a first portion of the trade of said second security in said one pair trade request, and at least one non-pair trade request in said order inventory, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread.19 A computer readable storage medium storing instructions for fulfilling a pair tra de request that, when executed by a computer, cause the computer to. receive a plurality of pair trade requests, comprising at least one pair trade request, wherein said pair trade request comprises a request to trade a first security, a request to trade a second security, and a request to trade said first security and said second security with a minimum spread limit, and wherein said first security and said second security each have a bid price and an ask price. determine the bid bid spread in the market of said first security and said second security. determine the ask ask spread in the market of said first security and said second security. determine that the minimum spread limit of said pair trade request is met by a range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said first security in said one pair trade request and at least a first non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread. execute a transaction between a first portion of the trade of said second security in said one pair trade request and at least a second non-pair trade request, provided that the minimum spread limit of said one pair trade request is met by said range of said bid bid spread and said ask ask spread and. repeat the executing steps until the pair trade request is fulfilled.20 The method of claim 19 wherein at least one non-pair trade request is selected from the group consisting of an external market order and an order from an inventory from a financial institution. CROSS-REFERENCE TO RELATED APPLICATIONS. This application is a divisional application of U S patent application Ser No 10 206,549, entitled Pair trading system and method , which was filed on Jul 25, 2002 now U S Pat No 7,412,415, which claims priority to U S provisional patent application Ser No 60 334,163 entitled Method and System for Trading Pairs of S ecurities that was filed on Nov 29, 2001 The contents of both applications are herein incorporated by reference. The following invention relates to a system and method for trading securities and, in particular, for a system and method of trading securities in pairs. A recognized strategy for trading securities is known as pair-trading Pair-trading is a non-directional investment strategy in which the investor identifies two securities having similar characteristics and the securities are currently trading at a price relationship that is out of their historical trading range The investor exploits the price relationship between the securities by buying the undervalued security while short-selling the overvalued security Because pair-trading is a market-neutral strategy, it is a particularly desirable strategy for investing in volatile markets. One context in which pair trading is useful is where an investor desires to take advantage of an arbitrage opportunity resulting from a merger betwee n two companies For example, Company A has announced a definitive agreement to acquire Company T in which case Company T shareholders will receive 0 5 shares of Company A stock for each share of Company T stock they own The investor desires to capture the spread between the offered consideration 0 5 shares of A and the price of T stock To do this, the investor buys shares in T stock and sells shares of A stock. For instance, if stock T is trading at 28 per share and stock A is trading at 60 per share, then the investor may execute a trade for 200,000 spreads by buying 200,000 shares of T stock and selling 100,000 shares of A stock After the merger takes place, the investor will cover the short position in stock A with the 100,000 shares of A stock the investors receives in exchange of the 200,000 shares the investor held of stock T Thus, by executing the pair trade, the investor locks in a 400,000 profit assuming that the merger goes through The process of executing a pair trade thus in cludes executing individual trades directed to each leg of the pair trade request An example of a system for executing trades for filling a pair trade request is the Quantex system from ITG of 380 Madison Avenue, New York, N Y 10017.A challenge in implementing a pair trade is to find a counterparty for a particular position an investor desires to establish while minimizing leg risk Typically, a large pair trade is performed off the market as a private transaction negotiated by a financial institution that services large clients For example, if an investor desires to execute a pair trade betting that a proposed merger between two companies will go through, the investor would approach a financial institution seeking an investor that is willing to bet against the merger The financial institution then acts as an intermediary between the two investors in which the investors establish equal and opposite positions in the stock of the proposed merger partners thereby completing the pair trade Thus by matching two pair trade requests so that the transactions associated with each of the pair trade legs are executed simultaneously, neither investor is exposed to leg risk that would otherwise result for the period of time between execution of the first leg and the second leg of the pair trade. There are numerous drawbacks associated with the prevalent pair-trading practice First, pair-trading is typically limited to clients of large financial institutions that have the ability to identify suitable counterparties for a particular pair trade This is especially the case when the pair trade involves a large amount of stock or illiquid stocks in which the only way to execute the trade and minimize leg risk is via an off the market transaction negotiated by a financial institution Also, because a pair-trade is typically negotiated by the parties with a financial institution as an intermediary, the process is often slow and inefficient Furthermore, pair-trading under current practice i s generally best suited for large clients seeking to establish large positions thereby providing the financial institutions with the economic incentive to execute the transaction Smaller clients, however, must rely on the markets for executing pair trades, which is unsuitable for illiquid stocks and also results in increased leg risk. Accordingly, it is desirable to provide a system and method for trading securities in pairs. SUMMARY OF THE INVENTION. The present invention is directed to overcoming the drawbacks of the prior art pair trading practices Under the present invention a method is provided for fulfilling a pair trade request and includes the steps of receiving a plurality of pair trade requests executing a transaction for a first portion of one of the plurality of pair trade requests and matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests. In an exemplary embodiment, the method includes the step of e xecuting a transaction for a first portion of one of the plurality of pair trade requests in an external market. In another exemplary embodiment, the method includes the step of executing a transaction for a first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request includes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and the method includes the steps of determining whether the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the second security that can be sold based on a bid size associated with the second security calculating an equivalent amount of the first security that can be bought based on the amount of the second security that can be sold adjusting the equivalent amount of the first security based on adjustment criteria calculating a purchase price for t he adjusted equivalent amount of the first security based on the spread limit executing an initiating order to buy the adjusted equivalent amount of the first security at the purchase price and executing a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the method includes the step of executing a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the method includes the steps of determining whether the ask price of the first security and the ask price of the second security and or the bid price of the first security and the bid price of the second security meet a spread limit determining an amount of the first security that can be bought based on an offer size associated with the first security calculating an equivalent amount of the second security that can be sold based on the amount of the second security that can be bought adjusting the equivalent amount of the second security based on adjustment criteria calculating a selling price for the adjusted equivalent amount of the second security based on the spread limit executing an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executing a covering order to purchase the amount of the first security. In another exemplary embodiment, the method includes the step of executing a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the adjustment criteria include a minimum amount and a maximum amount. In still yet another exemplary embodiment, the method includes the step of rounding the initiating order to a round lot size. In an exemplary embodiment, the method includes the step of executing a first portion of one of the plurality of pair trade requests in a plurality of tranches. In another exemplary embodiment, the one of the plurality of pair trade requests a nd the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of said plurality of trade requests has a second spread limit and wherein the method includes the steps of determining that a range of the first spread limit and the second spread limit overlaps with a market spread setting a spread level calculating prices for the first security and the second security that are within the market spread and based on the spread level and matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In yet another exemplary embodiment, the method includes the steps of calculating a mean between the first spread limit and the second spread limit and setting the spread level as the mean if the mean is within the market spread. In still yet another exemplary embodimen t, the method includes the step of identifying a spread amount that is closest to the mean and within the market spread and setting the spread level as the spread amount if the mean is not within the market spread. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and the method includes the steps of determining that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determining that market prices exist tha t are within the overlap determining a mismatch amount in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculating a cross amount for the first security and the second security selecting a crossing price for the first security and the second security that is within the overlap determining that the mismatch amount is available at the crossing price for the second security matching the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executing a transaction for the mismatch amount of the second security at the crossing price for the second security. In another exemplary embodiment, the method includes the step of determining that the mismatch amount is available in an external market at the crossing pr ice for the second security. In yet another exemplary embodiment, the method is performed by a financial institution having order inventory and includes the step of determining that the mismatch amount is available in the order inventory at the crossing price for the second security. In still yet another exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and the method includes the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In an exemplary embodiment, the method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of executing a transaction for a first portion of one of the plurality of pair trade requests, described above. In another exemplary embodiment, th e method includes the step of receiving a preference for filling at least some of the plurality of trade requests via the step of matching a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests, described above. Under the present invention, a method for fulfilling a pair trade request is provided and includes the steps of receiving a plurality of pair trade requests and matching at least a portion of one of the plurality of pair trade requests against another of the plurality of pair trade requests. Under the present invention, a system for fulfilling a pair trade request is provided, the system receiving a plurality of pair trade requests and includes a pair trading engine for executing a transaction for a first portion of one of the plurality of pair trade requests The system also includes a pair crossing network for matching a second portion of said one of the plurality of pair trade requests against another of the p lurality of pair trade requests. In an exemplary embodiment, the system includes a link to external markets and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests in the external markets. In another exemplary embodiment, the system includes a financial institution having an order inventory and wherein the pair trading engine executes the transaction for the first portion of one of the plurality of pair trade requests against the order inventory. In yet another exemplary embodiment, the pair trade request includes a first security having a bid price and an ask price and a second security having a bid price and an ask price, and wherein the pair trading engine determines whether the bid price of the first security and the bid price of the second security meet a spread limit determines an amount of the second security that can be sold based on a bid size associated with the second security calculates an equivalent amo unt of the first security that can be bought based on the amount of the second security that can be sold adjusts the equivalent amount of the first security based on adjustment criteria calculates a purchase price for the adjusted equivalent amount of the first security based on the spread limit executes an initiating order to buy said adjusted equivalent amount of the first security at the purchase price and executes a covering order to sell the amount of the second security. In still yet another exemplary embodiment, the pair trading engine executes a covering order to sell the amount of the second security at the bid price of the second security. In an exemplary embodiment, the pair trading engine determines whether the ask price of the first security and the ask price of the second security meet a spread limit determines an amount of the first security that can be bought based on an offer size associated with the first security calculates an equivalent amount of the second security t hat can be sold based on the amount of the second security that can be bought adjusts said equivalent amount of the second security based on adjustment criteria calculates a selling price for the adjusted equivalent amount of the second security based on the spread limit executes an initiating order to sell the adjusted equivalent amount of the second security at the selling price and executes a covering order to purchase the amount of the first security. In another exemplary embodiment, the pair trading engine executes a covering order to purchase the amount of the first security at the ask price of the first security. In yet another exemplary embodiment, the pair trading engine rounds the initiating order to a round lot size. In still yet another exemplary embodiment, the pair trading engine executes a first portion of one of the plurality of pair trade requests in a plurality of tranches. In an exemplary embodiment, the one of the plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit and the another of the plurality of trade requests has a second spread limit and wherein the pair crossing network determines that a range of the first spread limit and the second spread limit overlaps with a market spread sets a spread level calculates prices for the first security and the second security that are within the market spread and based on the spread level and matches the second portion of said one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices. In another exemplary embodiment, the pair crossing network calculates a mean between the first spread limit and the second spread limit and sets the spread level as the mean if the mean is within the market spread. In yet another exemplary embodiment, the pair crossing network identifies a spread amount that is closest to the mean and within the market spread and sets the spread level as the spread amount if the mean is not within the market spread. In still yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests include a first security and a second security, the one of the plurality of pair trade requests has a first spread limit, a buy ratio and a sell ratio, the another of the plurality of trade requests has a second spread limit, a buy ratio and a sell ratio and wherein the pair crossing network determines that the buy ratio and the sell ratio associated with the one of the plurality of trade requests does not equal the buy ratio and the sell ratio of the another of the plurality of trade requests and that an overlap exists between range of the first spread limit and the second spread limit and a market spread determines that market prices exist that are within the overlap determines a mismatch amou nt in the second security based on a difference between the buy ratio and the sell ratio associated with the one of the plurality of trade requests and the buy ratio and the sell ratio of the another of the plurality of trade requests calculates a cross amount for the first security and the second security selects a crossing price for the first security and the second security that is within said overlap determines that the mismatch amount is available at the crossing price for the second security matches the second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests based on the calculated prices and executes a transaction for the mismatch amount of the second security at the crossing price for the second security. In an exemplary embodiment, the pair crossing network determines that the mismatch amount is available in an external market at the crossing price for the second security. In another exemplary embodiment, the pair crossing network determines that the mismatch amount is available in the order inventory at the crossing price for the second security. In yet another exemplary embodiment, the one of said plurality of pair trade requests and the another of the plurality of pair trade requests indicate a number of spreads and wherein the pair crossing network matches a second portion of the one of the plurality of pair trade requests against another of the plurality of pair trade requests if the number of spreads is greater than a minimum number of spreads. In still yet another exemplary embodiment, the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via said pair crossing network, and the system further includes a portfolio manager in communications with the pair crossing network, the portfolio manager receiving the plurality of pair trade requests and routing the at least some pair trade requests to the pair crossing network according to the preference. In an exemplary embodiment, the system includes a pair trading engine for executing at least some of the plurality of pair trade requests, further includes a portfolio manager in communications with the pair trading engine and wherein the plurality of pair trade requests include at least some pair trade requests indicating a preference for execution via the pair trading engine, the portfolio manager receiving the plurality of pair trade requests and routing the at least some of the plurality of trade requests to the pair trading engine according to the preference. Under the present invention, a system for fulfilling a pair trade request is provided, wherein the system receives a plurality of pair trade requests and includes a pair crossing network for matching at least one of the plurality of pair trade requests against another of the plurality of pair trade requests. Accordingly, a method and a system are provided for trading pair securities. The invention accordingly com prises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims Other features and advantages of the invention will be apparent from the description, the drawings and the claims. DESCRIPTION OF THE DRAWINGS. For a fuller understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings, in which. FIG 1 is a block diagram of a system for trading securities in pairs according to the present invention. FIG 2 is a flowchart of the steps a pair trading engine included in the system of FIG 1 applies to fill a pair trade request. FIG 3 is a flowchart of the steps a pair crossing network included in the system of FIG 1 applies to fill a pair trade request. FIG 4 is a flowchart of a process by which the pair crossing network of the system of FIG 1 fills imperfectly matched orders and. FIG 5 i s a graph for identifying the market prices for two securities that meet the required spread limits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS. Referring now to FIG 1 there is shown a block diagram of a system 1 for trading securities in pairs according to the present invention System 1 receives pair trade requests from clients operating client access devices 7 and attempts to fill the pair trade requests according to the parameters associated with the particular pair trade request System 1 includes two different subsystems for filling pair trade requests a pair trading engine 3 and a pair crossing network 5 As will be described below, pair trading engine 3 receives a pair trade request and attempts to fill in whole or in part the trade request by executing the appropriate trades in an external market 13 that may include, by way of non-limiting example, the New York Stock Exchange, the NASDAQ or any other financial market Pair trading engine 3 may also fill in whole or in part a pair trade request by executing a transaction against order inventory 11 of non-pair trade requests controlled by the financial institution that is operating system 1 In addition, pair trading engine may also fill in whole or in part a pair trade request by forwarding the trade request to pair crossing network 5 for matching with other pair trade requests. Likewise, pair crossing network 5 receives a pair trade request and fulfills in whole or in part the request by matching it against another pair trade request received by pair crossing network 5 by matching the request against inventory 11 controlled by the financial institution and or by forwarding the trade request to pair trading engine 3 for execution in external markets 13.System 1 also includes a portfolio manager 9 that may be, for example, a software program executing on a computer system that receives the pair trade requests from client access device 7 and presents the trade request to either pair trading engine 3 pair crossi ng network 5 or both, depending on the trade parameters set by the client Also, the client may query portfolio manager 9 regarding the status of any pair trade request the client has presented to system 1.In operation, system 1 may fulfill a pair trade request either using pair trading engine 3 or pair crossing network 5 or a combination of the two For example, a pair trade request received by system 1 may be completely filled by pair trading engine 3 as follows. Assume a case where XYZ is taking over ABC and is offering 0 575 shares of XYZ for each ABC share and investor Arb wants to invest in the price difference between ABC stock and XYZ stock To take advantage of the price difference, Arb wants to lock in the difference between the value offered 0 575 XYZ stock and the value of ABC stock by buying ABC stock and selling XYZ stock subject to the condition that ABC 0 575 XYZ 1 19 i e Arb desires to capture a 1 19 difference between XYZ s takeover offer and ABC s share price. In order to fill this pair trade, Arb presents a pair trade request to portfolio manager 9 using client access device 7 The pair trade request typically includes a number of parameters that define the pair trade and that also may be used by portfolio manager 9 in determining how the pair trade request is to be filled Arb typically indicates in the trade request the number of spreads the Arb desires to invest in and also provides a minimum and maximum share amount that he is willing to trade per tranche. For example, Arb may indicate a desire to invest in 100,000 spreads and may only wish to trade the spread 3,000-8,000 shares at a time Arb generally sets this tranche size range based on the liquidity and volatility of ABC stock and XYZ stock Arb may set a larger minimum tranche size if ABC stock and XYZ stock are fairly liquid stocks because higher liquidity increases the likelihood that a larger tranche size will be executed Arb may set a lower maximum tranche size if XYZ stock and ABC stock are volatile stocks so as to limit the leg risk associated with executing a pair trade. Yet another pair trade parameter Arb provides is the spread limit in the above case 1 19 which is the amount Arb desires to capture in the trade Arb does not have to provide, however, the discrete prices at which trades for ABC and XYZ stock are to be executed as these prices are calculated by pair trading engine 3 and or pair crossing network 5 , as will be described below. Referring now to FIG 2 there is shown a flowchart describing the steps pair trading engine 3 applies to fill a pair trade request The flowchart in FIG 2 is based on the above example and the market data listed in Table 1 below. Initially, in Step 201 pair trading engine 3 determines whether the bid bid prices or ask ask prices of ABC and XYZ stock, respectively, meet the spread limit requirement of the particular pair trade request In this case the bid bid spread is 1 4375 122 50 0 575 69 and the ask ask spread is 1 1969 122 625 0 575 69 3125 so that each spread is less than the spread limit of 1 19, as is required for this particular trade Once it is determined that either the bid bid spread or the ask ask spread meets the spread limit, then in Step 202 it is determined as is indicated in Table 1 how much XYZ stock can be sold at the bid and how much ABC stock can be bought at the ask In an exemplary embodiment, the client may specify whether the bid bid spread, the ask ask spread or either the bid bid or the ask ask spread must exceed the indicated spread limit for a transaction to proceed If neither the bid bid spread nor the ask ask spread meets the spread limit, the process waits a period of time for example 0 10 seconds and returns to Step 201 to again test whether the bid bid spread or the ask ask spread meets the spread limit. Next, in step 203 an equivalent amount of stock that can be sent into the market i e bought sold in the market is calculated for a spread based on the bid bid price spread and or the as k ask price spread that meets the spread limit In this example, if a maximum of 10,000 shares of XYZ stock can be sold into the market i e the XYZ bid size then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 17,391 10,000 0 575 shares of ABC stock are to be bought in order to execute a balanced pair trade Likewise, if a maximum of 1,500 shares of ABC stock can be bought in the market i e the ABC ask size , then, based on the ABC XYZ ratio of 1 0 575 in this case , a total of 863 1500 0 575 shares of XYZ stock are to be sold in order to execute a balanced pair trade. Next, in Step 204 the pair trade share amounts calculated in Step 203 are adjusted to conform to the wave maximum and minimum parameters i e the maximum minimum tranche size included in the pair trade request as well as market round lot limits In the above example, the amount of ABC shares to be bought that was calculated based on the XYZ bid size i e 17,391 is first rounded to an even lot size i e 17,400 a nd then reduced to the maximum tranche size of 8000 Also, the amount of XYZ shares to be offered that was calculated based on the ABC ask size i e 863 is first rounded to an even lot size i e 900 and then increased to 1,700 shares to meet the minimum tranche size of 3000 3000 0 575 1777 In an exemplary embodiment the minimum and maximum tranche size is scaled by the particular ratio for example, in the above case, the tranche sizes for XYZ stock is scaled by 0 575 In another embodiment, the maximum minimum tranche size is used for each security in the pair trade request without scaling In yet another exemplary embodiment, the pair trade request includes a separate maximum minimum tranche for each security. Once the share amounts for the pair trade are calculated, in Step 205 the share prices that are needed to meet the spread limit of the pair trade request are calculated For example, for a pair trade based on the bid bid price spread, in order to meet the spread limit of 1 19 credit, t he price at which ABC stock is to be bid should be no greater than 69 2475 122 50 0 575 1 19 a share Likewise, for a pair trade based on the ask ask price spread, in order to meet the spread limit, the price at which XYZ stock is to be offered should be greater than or equal to 122 6130 69 3125 1 19 0 575 a share. Next, once the pair trade share amounts and share prices have been calculated, in Step 206 pair trading engine 3 sends initiating orders to external markets 13 in order to fill the pair trade request The initiating orders may include an initiating order for executing a pair trade based on the bid bid spread in this case a bid for 8,000 shares of ABC stock at 69 2475 and or an initiating order for executing a pair trade based on the ask ask spread in this case an offer of 1,700 shares of XYZ stock at 122 6130.Finally, as the initiating orders sent to external markets 13 in Step 207 get filled, pair trading engine 3 automatically sends into the market the covering side of the pa ir trade So, for example, as the initiating order of buying 8,000 shares of ABC stock at 69 2475 gets filled, pair trading engine 3 sends an order to external markets 13 to sell 4,600 8,000 0 575 shares of XYZ stock at 122 50.In an exemplary embodiment, the client s pair trade request includes threshold amounts that indicate the amount of variance in stock price and or share amount the client is willing to absorb For example, if in the process of covering the initiating order the price of XYZ stock dips to 122 49 in which case the spread limit of the pair trade would drop to 1 18 , then pair trading engine 3 would still sell XYZ stock at the price of 122 49 if the 0 01 difference was within the threshold amount included in the pair trade request Similarly, the pair trade request may include threshold amounts for any other pair trade parameter, including by way of non-limiting example, the number of spreads to be purchased and the tranche sizes If, however, a particular threshold amount indicated by the client is exceeded for any given pair trade parameter, then pair trading engine 3 would attempt to cancel the initiating order and or the covering order that may be possible if the orders have not yet reached the market or have not yet been filled In such a case, pair trading engine 3 would then repeat the above analysis for determining suitable initiating and cover orders. To fill a pair trade request, pair trading engine 3 executes trades utilizing the method described above Typically, pair trading engine 3 tranches a pair trade request and trades piece-meal in external markets 13 In certain cases, however, it may be difficult to fill a trade request by executing several transactions in external markets 13 either because the pair trade request is for a very large number of spreads or includes stocks that are illiquid in which cases pair trading engine 3 may be ineffective in filling the pair trade request Also, in certain situations, a client wishing to remain anonym ous may indicate in the pair trade request a preference that no orders be sent to external markets 13 In these circumstances, portfolio manager 9 may route the particular pair trade request to pair crossing network 5.Referring now to FIG 3 there is shown a flowchart illustrating the steps pair crossing network 5 applies to fill a pair trade request The flowchart in FIG 3 is based on the above example and the market data listed in Table 2 below. Spread Limit as defined by 0 575 XYZ ABC. Continuing the previous example, assume the pair trade request issued by Arb for 100,000 spreads was half-filled by pair trading engine 3 Also, assume that system 1 receives a pair trade request from Antiarb that indicates a desire to sell 30,000 shares of ABC and buy 17,200 shares a ratio of 1 0 575 and also indicates a spread limit of 1 30 i e ABC 0 575XYZ 1 30 In this case Arb and Antiarb s orders are complimentary in the primary order elements securities, ratios and buy versus sell Also, Antiarb is willing to pay 0 11 per spread more than Arb is demanding from the marketplace Based on these parameters, there is an opportunity for Arb s and Antiarb s trade requests to be filled via pair crossing network 5.If Antiarb s pair trade request was marked for trading by pair trading engine 3 then portfolio manager 9 sends Antiarb s order to pair trading engine 3 for execution Pair trading engine 3 then sends the parameters of Antiarb s trade request, as well as all orders waiting for execution in pair trading engine 3 to pair crossing network 5 Pair crossing network 5 will recognize as described above that there is a crossing opportunity between Arb s order and Antiarb s order In this case, pair crossing network 5 then directs pair trading engine 3 to suspend the execution of Antiarb s order in the amount that can be crossed by pair crossing network 5 30,000 spreads in this case In addition, pair trading engine 3 routes a cross amount of 30,000 spreads from Arb s order to pair crossing network 5 for crossing against Antiarb s order At this point, the pair crossing network 5 crosses the Antiarb order against a portion of Arb s order, as follows. Assume the prevailing market conditions at the time of the cross are as shown in Table 3 Furthermore, Table 3 indicates the XYZ Ratio-Adjusted Value for both the bid and ask prices based on the conversion ratio of 1 0 575 Based on the XYZ Ratio-Adjusted Values, a Bid Ask Spread Range i e the spread provided for a cross between the bid price of ABC stock and the XYZ Ratio-Adjusted ask price of 1 3863 is calculated and an Ask Bid Spread Range i e the spread provided for a cross between the ask price of ABC stock and the XYZ Ratio-Adjusted bid price of 1 05 is calculated. To perform the cross, in Step 301 pair crossing network 5 first determines whether the range of spread limits associated with Arb s and Antiarb s trade requests i e 1 30- 1 19 coincides with the range of the prevailing market spread 1 3863- 1 05 In this example, the range of spread limits does coincide with the prevailing market spread because at least a portion of the spread limit range overlaps with a portion of the market spread Thus, a cross can occur. Next, in Step 302 pair crossing network 5 calculates the mean of Arb s and Antiarb s spread order limit which is 1 30 1 19 2 1 245 and determines whether the mean is within the range of the market spread i e 1 3863- 1 05 If it is, then in Step 303 pair cros sing network 5 calculates the prices at which to cross The prices must be within the current markets for ABC stock and XYZ stock, and satisfy market uptick requirements for short sales , and provide a spread that is equal to the spread level calculated above For example, with the inside market for ABC stock at 70 00-70 25 and the inside market for XYZ stock at 124 00-124 15, a cross price of 70 11 for ABC stock and 124 096 for XYZ stock provides the spread of 1 2452 thereby meeting the requirement of both Arb s and Antiarb s trade request Finally, in Step 304 pair crossing network 5 crosses 30,000 shares of ABC stock at 70 11 with Arb buying and Antiarb selling and 17,200 shares of XYZ at 124 096 with Arb selling and Antiarb buying. If it is determined in Step 302 that the mean of Arb s and Antiarb s spread order limits does not fall within the range of the market spread, then in Step 305 the spread closest to the mean of the two spread limits that is also within the market spread is ca lculated For example, if the market spread is 1 3863- 1 28, then the mean of the two spread limits 1 245 is not within the market spread In such a case, 1 28 is selected as the spread level that is closest to the mean and within the market spread In an exemplary embodiment, the spread level at which Arb and Antiarb cross can be determined in any other suitable manner as long as the spread level is within the market spread and within the range of spread limits indicated in the pair trade requests. Once the spread level is determined, the method proceeds to Step 303 in which pair crossing network 5 calculates prices to cross at that are within the current markets for ABC stock and XYZ stock and that meet the calculated spread level In the case where the calculated spread level is 1 28, the cross will occur at a price of 70 08 for ABC stock and 124 1043 for XYZ stock Finally, the method proceeds to Step 304 in which pair crossing network 5 performs the cross between Arb and Antiarb. Once a pair trade request is filled or partially filled , the transaction details are reported to portfolio manager 9 and made available to the client operating client access device 7.In the previous example, pair crossing network 5 crosses orders in which both Arb and Antiarb desire to trade the same pair of securities in the same ratio In an exemplary embodiment, pair crossing network 5 executes a cross between two pair trade requests that are not perfectly matched. For example, assume that pair crossing network 5 receives the pair trade requests as shown in Table 4 Note that these two pair trade requests are imperfectly matched because each trade request uses a different ratio between ABC and XYZ stock. Arb s Spread Limit is defined by 0 575 XYZ ABC Antiarb s Spread Limit is defined by 0 6 XYZ ABC. Also, assume the market in ABC and XYZ stocks at the time the pair trade requests are received by pair crossing network 5 is as described in Table 5 below. Arb s XYZ Ratio-Adjusted Value. Arb s Dollar Range. AntiArb s XYZ Ratio-Adjusted Value. AntiArb s Dollar Range. Referring now to FIG 4 there is shown a flowchart illustrating a process by which pair crossing network 5 fills these imperfectly matched order First, in Step 401 pair crossing network 5 determines whether Arb s buy security equals Antiarb s sell security and whether Arb s sell security equals Antiarb s buy security If both conditions are not met, then a cross between the two orders cannot occur If the two conditions are met, then in Step 402 it is determined whether Arb s buy ratio equals Antiarb s sell ratio and whether Arb s sell ratio equals Antiarb s buy ratio If these ratios are the same, then pair crossing network 5 proceeds t o cross the two orders as described in the example above Note that for a cross to occur at this stage does not require the ratios themselves to match but rather that the ratios of the ratios match for e g a ratio of 2 3 matches a ratio of 0 667 1.If, however, the two ratios are not equal as in this case where Arb s sell ratio does not equal Antiarb s buy ratio , then in Step 403 pair crossing network determines whether there is an overlap between Arb s and Antiarb s spread limit that also falls within the bid ask market for ABC and XYZ stock To make such a determination, pair crossing network 5 calculates whether there are market prices for both ABC and XYZ stock that satisfy the following inequalities L 1 Ratio A ABC Ratio B XYZ and 1 L 2 Ratio C ABC Ratio D XYZ 2 Where L 1 is Arb s spread limit of 1 19 credit, L 2 is Antiarb s spread limit of 4 40 debit, RatioA is Arb s buy ratio of 1 1, RatioB is Arb s sell ratio of 1 0 575, RatioC is Antiarb s sell ratio of 1 1 and RatioD is Antiar b s buy ratio of 1 0 6.Referring now to FIG 5 there is shown a graph 51 that depicts market prices for ABC and XYZ stock that meet the spread limits of Arb and Antiarb In graph 51 the x-axis represents the prices for XYZ stock while the y-axis represents the prices for ABC stock Graph 51 includes a shaded area 53 that is the universe of market prices for ABC and XYZ stock that could satisfy the spread trade involving those stocks Also included in graph 53 is a spread limit line L 1 inequality 1 , above that represents the spread limit associated with Arb and a spread limit line L 2 inequality 2 , above that represents the spread limit associated with Antiarb Thus, the solution set of market prices that satisfies inequalities 1 and 2 is the portion of dark shared area 53 that falls between spread limit line L 1 and spread limit line L 2 In this example, a cross at a share price for ABC of 70 14 and a share price of 124 15 for XYZ stock meets the investor s spread limits and falls within the market prices for ABC and XYZ stock. If it is determined that no share prices for both ABC and XYZ stock satisfy Arb s and Antiarb s spread limits, then no cross can occur If such share prices do exist, then in Step 404 it is determined which of the investors desires to transact in fewer shares of ABC stock and a mismatch in share amounts caused by the differing ratios is determined In our example, Antiarb desires to sell fewer ABC shares than Arb desires to buy 30,000 vs 50,000 Then, in Step 405 pair crossing network 5 determines the number of XYZ shares that can be crossed between Arb and Antiarb based on the maximum amount of ABC shares that can be crossed 30,000 in this example Based on the Antiarb ABC order quantity of 30,000 shares, the maximum number of XYZ shares that Arb will cross with Antiarb is.30 000 Arb XYZ Ratio Arb ABC Ratio 30 000 0 575 1 17 300 17 250 rounded to an even lotsize. While the maximum quantity of XYZ shares that Arb will cross is 17,300, Antiarb s trade request indicates a desire to cross 18,000 shares To overcome this imbalance, in Step 406 pair crossing network 5 is in communications with external markets 13 for determining whether the excess 700 XYZ shares needed to satisfy Antiarb s trade request can be transacted for in external markets 13 In an exemplary embodiment, pair crossing network 5 makes this determination by issuing a query to pair trading engine 3 as to whether 700 shares of XYZ stock can be bought in external markets 13 Because, as indicated in Table 5, 3,000 shares of XYZ stock are offered at 124 15, pair trading engine 3 responds to pair crossing network 5 that the 700 shares needed to balance the cross between Arb and Antiarb are available from external markets 13 at 124 15.Next, in Step 407 pair crossing network calculates the cross prices that are necessary such that Arb and Antiarb achieve their respective spread limits while also incorporating the excess 700 shares of XYZ stock that must be purchased from exte rnal markets 13 at 124 15 to satisfy Antiarb s trade request An example of such cross prices that meet these criteria is a price of 70 14 for ABC stock and a price of 124 15 for XYZ stock. Once the cross prices are calculated, in Step 408 pair crossing network 5 crosses 30,000 shares of ABC stock and 17,300 shares of XYZ stock between Arb and Antiarb and also buys 700 shares of XYZ stock at 124 15 in external markets 13 on behalf of Antiarb Thus, both Arb and Antiarb s pair trade requests are satisfied. Alternatively, the entire 18,000 shares of XYZ stock may be crossed thereby fully satisfying Antiarb s trade request In such a case, the ratio mismatch is addressed by Arb purchasing an additional 1200 700 0 575 rounded to a lotsize shares of ABC stock from external market 13 or from firm inventory 11.Once the trade is completed, the details of the transaction are provided to portfolio manager 9 to report the transaction details to the investors. In an exemplary embodiment, a pair order or portion thereof may be filled against an internal inventory 11 of trade requests maintained by the financial institution operating system 1 For example, in the previous example in which an excess of 700 shares of XYZ stock needs to be purchased in order for a match i e cross between Arb and Antiarb s trade requests to occur, instead of determining whether the 700 shares are available in external markets 3 pair crossing network 5 examines firm inventory 11 to determine whether the shares are available at the required price Likewise, in cases where pair trading engine 3 desires to execute a pair trade based on orders to be sent to external markets 13 pair trading engine 3 may first determine whether the order can be filled, in whole or in part, using trade requests pending in firm inventory 11 Generally, the advantages of filling an order using pending trade requests in firm inventory 11 is that execution is faster, transaction costs are lower and leg risk is minimized. In another exempl ary embodiment, a client s pair trade request may also include a minimum number of spreads that can be traded in pair crossing network 5 Also, pair crossing network 5 may be designed to require a minimum share amount for a cross to occur A minimum number of spreads that can be traded may be provided in order to reduce the distractions and booking costs associated with numerous smaller trades that may exceed the benefits of a de minimis fill. In another exemplary embodiment, portfolio manager 9 publishes the inside cross market for any pair that a client has selected for crossing in pair crossing network 5 In still another exemplary embodiment, the client has the option for each pair trade selected for crossing in pair crossing network 5 to designate that the order should be reflected in the published inside cross market This inside cross market consists of the tightest spread bid and offer and corresponding bid size and offer size from all client pair orders pending in pair crossing net work 5 In this way, a client can assess the likelihood and timing of a pair trade request being filled by pair crossing network 5 Also, by publishing the client s spread interest, others seeking liquidity can trade at the client s level. In an exemplary embodiment, the client can designate each pair order designated for pair trading engine 3 and or pair crossing network 5 for Broker Negotiation If Broker Negotiation is designated, the client s broker-dealer sales representative is notified of the client s spread order thereby prompting the broker-dealer to solicit a complementary, agency order from another client The client may also designate each pair order for Broker Facilitation in which case the client allows the broker-dealer to act principally to fill the client s order. In summary, the advantages to a client of using pair trading engine 3 is that pair trading engine 3 allows the client to trade a spread order while limiting leg risk or the risk of missing a targeted spread level T his is accomplished by breaking the total order into tranches of sizes proportionate to the market, subject to user minimums and maximums, that can be traded in external markets 13 or against firm inventory 11 Orders executed via pair trading engine 3 however, are typically of a lower traded volume because trading is constrained to the liquidity available in the market In contrast, trades executed via pair crossing network 5 are not constrained by market liquidity and do not have to be tranched to minimize leg risk In particular, the benefits of filling a pair trade request via pair crossing network 5 are as follows. Elimination of Leg Risk Pair crossing network 5 potentially provides a deeper well of liquidity because the trades are brokered, as a spread, directly between spread investors via a central clearing facility Moreover, the introduction and use of a pair trading facility eliminates the leg risk described above without a sacrifice of liquidity. Large Transactions Only Certain l arge investors may prefer to use pair crossing network 5 rather than pair trading engine 3 to avoid having a trade request broken up into numerous small executions For example, sudden, brief moves in one of the two stocks included in the pair trade request may cause pair trading engine 3 to issue numerous small executions to fill the request While a small investor may welcome capturing these small opportunities, a large investor may find such small executions to be more of a nuisance than a service. Price Setting versus Price Taking Large investors seeking liquidity may prefer to set their price via the pair crossing network 5 Also, other spread investors looking for liquidity can use pair crossing network 5 to monitor and trade with the large investor at the large investor s level While client orders directed to pair trading engine 3 can designate a spread limit, such orders are essentially price-takers as the market reaches the desired level, the orders are executed Moreover, the pair trading engine tranching mechanism creates relatively small orders, allowing institutional flows to move the individual stocks As a result, the small, tranched orders generated by pair trading engine 3 can become overpowered by single-name institutional flows In addition, orders designated solely for pair trading engine 3 and not for pair crossing network 5 are not published to a central quote facility such as by portfolio manager 9 thereby preventing other spread traders from knowing the size and limit of a pair trading engine order. Illiquid Stocks vs Liquid Stocks Spreads that include one or two illiquid stocks are difficult to fill using pair trading engine 3 alone Because illiquid stocks often demonstrate small bid and ask sizes and wide bid-ask spreads, pair trading engine 3 will typically only issue market orders having small quantities subject to user minimums and maximums that presents the client with greater leg risk from mid-trade changes in the bid-ask prices In contrast, o rders routed to price crossing network 5 are not confined by liquidity in the market place thereby allowing large crosses between spread traders in illiquid spreads. Accordingly, a system and method for trading pair securities is provided in which the client receives the benefits of having a pair order filled by either pair trading engine 3 pair crossing network 5 or a combination of both. A number of embodiments of the present invention have been described Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention Based on the above description, it will be obvious to one of ordinary skill to implement the system and methods of the present invention in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device Each computer program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired and in any case, the language may be a compiled or interpreted language Suitable processors include, by way of example, both general and special purpose microprocessors Furthermore, alternate embodiments of the invention that implement the system in hardware, firmware or a combination of both hardware and software, as well as distributing modules and or data in a different fashion will be apparent to those skilled in the art and are also within the scope of the invention In addition, it will be obvious to one of ordinary skill to use a conventional database management system such as, by way of non-limiting example, Sybase, Oracle and DB2, as a platform for implementing the present invention Also, network access devices can comprise a personal computer executing an operating system such as Microsoft Windows , Unix , or Apple Mac OS , as well as software applications, such as a JAVA program or a web browser Access devices can also be a terminal device, a palm-type computer, mobile WEB access device or other device that can adhere to a point-to-point or network communication protocol such as the Internet protocol Computers and network access devices can include a processor, RAM and or ROM memory, a display capability, an input device and hard disk or other relatively permanent storage Accordingly, other embodiments are within the scope of the following claims. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process, in a described product, and in the construction set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shown in the accompanying drawing shall b e interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.
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