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C $Header: /u/u3/gcmpack/MITgcm/model/src/port_rand.F,v 1.3 2001/09/26 18:09:16 cnh Exp $ |
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C $Name: $ |
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C Portable random number generator |
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#undef _USE_INTEGERS |
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! ============================================================================== |
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CBOP |
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C !ROUTINE: port_rand |
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C !INTERFACE: |
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real*8 function port_rand(seed) |
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C !DESCRIPTION: \bv |
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C Portable random number generator |
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C \ev |
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C !LOCAL VARIABLES: |
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implicit none |
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integer nff |
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parameter(nff=55) |
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#ifdef _USE_INTEGERS |
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integer mbig,mseed,mZ,seed |
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#else |
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real*8 mbig,mseed,mz,seed |
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#endif |
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real*8 fac |
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#ifdef _USE_INTEGERS |
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parameter (mbig=1000000000,mz=0,fac=1./mbig) |
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data mseed/161803398/ |
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#else |
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parameter (mbig=4000000.,mz=0.,fac=1./mbig) |
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data mseed/1618033./ |
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#endif |
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integer i,ii,inext,inextp,k,idum |
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parameter(idum=-2) |
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#ifdef _USE_INTEGERS |
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integer mj,mk,ma(nff) |
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#else |
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real*8 mj,mk,ma(nff) |
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#endif |
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logical firstCall |
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save firstCall,inext,inextp,ma |
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data firstCall /.true./ |
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CEOP |
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! ------------------------------------------------------------------------------ |
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mseed = seed |
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if(firstCall)then |
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firstCall=.false. |
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mj=mseed-iabs(idum) |
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mj=mod(mj,mbig) |
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ma(nff)=mj |
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mk=1 |
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do i=1,nff-1 |
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ii=mod(21*i,nff) |
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ma(ii)=mk |
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mk=mj-mk |
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if(mk.lt.mz)mk=mk+mbig |
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mj=ma(ii) |
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enddo |
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do k=1,4 |
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do i=1,nff |
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ma(i)=ma(i)-ma(1+mod(i+30,nff)) |
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if(ma(i).lt.MZ)ma(i)=ma(i)+mbig |
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enddo |
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enddo |
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inext=0 |
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inextp=31 |
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endif |
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inext=mod(inext,nff)+1 |
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inextp=mod(inextp,nff)+1 |
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mj=ma(inext)-ma(inextp) |
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if(mj.lt.MZ)mj=mj+mbig |
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ma(inext)=mj |
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port_rand=mj*fac |
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return |
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! ------------------------------------------------------------------------------ |
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end |
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! ============================================================================== |
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|
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! ============================================================================== |
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subroutine port_ranarr(n,arr) |
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implicit none |
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integer n,i |
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real arr(n) |
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real*8 port_rand,seed |
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seed=1618033.0d0 |
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! ------------------------------------------------------------------------------ |
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do i=1,n |
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arr(i)=port_rand(seed) |
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enddo |
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|
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return |
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! ------------------------------------------------------------------------------ |
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end |
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! ============================================================================== |
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