36 lines
849 B
Fortran
36 lines
849 B
Fortran
FUNCTION poidev(xm,idum)
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INTEGER idum
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REAL poidev,xm,PI
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PARAMETER (PI=3.141592654)
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CU USES gammln,ran1
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REAL alxm,em,g,oldm,sq,t,y,gammln,ran1
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SAVE alxm,g,oldm,sq
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DATA oldm /-1./
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if (xm.lt.12.)then
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if (xm.ne.oldm) then
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oldm=xm
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g=exp(-xm)
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endif
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em=-1
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t=1.
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2 em=em+1.
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t=t*ran1(idum)
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if (t.gt.g) goto 2
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else
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if (xm.ne.oldm) then
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oldm=xm
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sq=sqrt(2.*xm)
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alxm=log(xm)
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g=xm*alxm-gammln(xm+1.)
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endif
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1 y=tan(PI*ran1(idum))
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em=sq*y+xm
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if (em.lt.0.) goto 1
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em=int(em)
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t=0.9*(1.+y**2)*exp(em*alxm-gammln(em+1.)-g)
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if (ran1(idum).gt.t) goto 1
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endif
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poidev=em
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return
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END
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