ran2.f

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      FUNCTION ran2(idum)
*
*       Random number generator (Press et al. second edition).
*       ------------------------------------------------------
      implicit double precision(a-h,o-z)
      INTEGER idum,im1,im2,imm1,ia1,ia2,iq1,iq2,ir1,ir2,ntab,ndiv
      INTEGER idum2,j,k,iv,iy
      common/rand2/  iy,idum2,iv(32),ixyz(65)
c      REAL ran2,AM,EPS,RNMX
      parameter(im1=2147483563,im2=2147483399,am=1.d0/im1,imm1=im1-1,
     *ia1=40014,ia2=40692,iq1=53668,iq2=52774,ir1=12211,ir2=3791,
     *ntab=32,ndiv=1+imm1/ntab,eps=1.2d-7,rnmx=1.d0-eps)
*     INTEGER idum2,j,k,iv(NTAB),iy
*     SAVE iv,iy,idum2
*     DATA idum2/123456789/, iv/NTAB*0/, iy/0/
*     DATA  IY,IDUM2,IV,IXYZ  /0,123456789,32*0,65*0/
      if (idum.le.0) then
        idum=max(-idum,1)
        idum2=idum
        do 11 j=ntab+8,1,-1
          k=idum/iq1
          idum=ia1*(idum-k*iq1)-k*ir1
          if (idum.lt.0) idum=idum+im1
          if (j.le.ntab) iv(j)=idum
11      continue
        iy=iv(1)
      endif
      k=idum/iq1
      idum=ia1*(idum-k*iq1)-k*ir1
      if (idum.lt.0) idum=idum+im1
      k=idum2/iq2
      idum2=ia2*(idum2-k*iq2)-k*ir2
      if (idum2.lt.0) idum2=idum2+im2
      j=1+iy/ndiv
      iy=iv(j)-idum2
      iv(j)=idum
      if(iy.lt.1)iy=iy+imm1
      ran2=min(am*iy,rnmx)
      return
      END
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