68 lines
1.9 KiB
FortranFixed
68 lines
1.9 KiB
FortranFixed
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*dk,ran2_lg
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function ran2_lg(idum)
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C
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C #####################################################################
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C
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C PURPOSE -
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C
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C RAN2_LG returns a uniform random deviate between 0.0 and 1.0
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C (exclusive of endpoint values). Initialize with IDUM equal
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C to a negative integer and do not change thereafter.
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C
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C INPUT ARGUMENTS -
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C
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C idum - Initialize this seed with a negative integer
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C and do not change thereafter.
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C
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C OUTPUT ARGUMENTS -
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C
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C ran2_lg - uniform random deviate between 0.0 and 1.0
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C
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C CHANGE HISTORY -
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C
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C $Log: ran2_lg.f,v $
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C Revision 2.00 2007/11/09 20:03:59 spchu
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C Import to CVS
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C
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CPVCS
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CPVCS Rev 1.0 Wed Jul 07 13:46:32 1999 kuprat
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CPVCS Initial revision.
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implicit none
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integer idum,im1,im2,imm1,ia1,ia2,iq1,iq2,ir1,ir2,ntab,ndiv
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real*8 ran2_lg,am,eps,rnmx
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c
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c... Note: RNMX should approximate the largest floating point
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c... value that is less than one.
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c
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parameter (im1=2147483563,im2=2147483399,am=1.d0/im1,imm1=im1-1,
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& ia1=40014,ia2=40692,iq1=53668,iq2=52774,ir1=12211,
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& ir2=3791,ntab=32,ndiv=1+imm1/ntab,eps=1.e-14,rnmx=1.d0-eps)
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integer idum2,j,k,iv(ntab),iy
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save iv,iy,idum2
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data idum2/123456789/, iv/ntab*0/, iy/0/
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if (idum.le.0) then
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idum=max(-idum,1)
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idum2=idum
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do j=ntab+8,1,-1
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k=idum/iq1
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idum=ia1*(idum-k*iq1)-k*ir1
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if (idum.lt.0) idum=idum+im1
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if (j.le.ntab) iv(j)=idum
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enddo
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iy=iv(1)
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endif
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k=idum/iq1
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idum=ia1*(idum-k*iq1)-k*ir1
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if (idum.lt.0) idum=idum+im1
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k=idum2/iq2
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idum2=ia2*(idum2-k*iq2)-k*ir2
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if (idum2.lt.0) idum2=idum2+im2
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j=1+iy/ndiv
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iy=iv(j)-idum2
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iv(j)=idum
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if (iy.lt.1) iy=iy+imm1
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ran2_lg=min(am*iy,rnmx)
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return
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end
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