initgn.f

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      SUBROUTINE initgn(isdtyp)
C**********************************************************************
C
C     SUBROUTINE INITGN(ISDTYP)
C          INIT-ialize current G-e-N-erator
C
C     Reinitializes the state of the current generator
C
C     This is a transcription from Pascal to Fortran of routine
C     Init_Generator from the paper
C
C     L'Ecuyer, P. and Cote, S. "Implementing a Random Number Package
C     with Splitting Facilities." ACM Transactions on Mathematical
C     Software, 17:98-111 (1991)
C
C
C                              Arguments
C
C
C     ISDTYP -> The state to which the generator is to be set
C
C          ISDTYP = -1  => sets the seeds to their initial value
C          ISDTYP =  0  => sets the seeds to the first value of
C                          the current block
C          ISDTYP =  1  => sets the seeds to the first value of
C                          the next block
C
C                                   INTEGER ISDTYP
C
C**********************************************************************
C     .. Parameters ..
      INTEGER*4 numg
      parameter(numg=32)
C     ..
C     .. Scalar Arguments ..
      INTEGER*4 isdtyp
C     ..
C     .. Scalars in Common ..
      INTEGER*4 a1,a1vw,a1w,a2,a2vw,a2w,m1,m2
C     ..
C     .. Arrays in Common ..
      INTEGER*4 cg1(numg),cg2(numg),ig1(numg),ig2(numg),lg1(numg),
     +        lg2(numg)
      LOGICAL qanti(numg)
C     ..
C     .. Local Scalars ..
      INTEGER*4 g
C     ..
C     .. External Functions ..
      LOGICAL qrgnin
      INTEGER*4 mltmod
      EXTERNAL qrgnin,mltmod
C     ..
C     .. External Subroutines ..
      EXTERNAL getcgn
C     ..
C     .. Common blocks ..
      COMMON /globe/m1,m2,a1,a2,a1w,a2w,a1vw,a2vw,ig1,ig2,lg1,lg2,cg1,
     +       cg2,qanti
C     ..
C     .. Save statement ..
      SAVE /globe/
C     ..
C     .. Executable Statements ..
C     Abort unless random number generator initialized
      IF (qrgnin()) GO TO 10
      WRITE (*,*) ' INITGN called before random number generator ',
     +  ' initialized -- abort!'
      CALL xstopx
     + (' INITGN called before random number generator initialized')
 
   10 CALL getcgn(g)
      IF ((-1).NE. (isdtyp)) GO TO 20
      lg1(g) = ig1(g)
      lg2(g) = ig2(g)
      GO TO 50
 
   20 IF ((0).NE. (isdtyp)) GO TO 30
      CONTINUE
      GO TO 50
C     do nothing
   30 IF ((1).NE. (isdtyp)) GO TO 40
      lg1(g) = mltmod(a1w,lg1(g),m1)
      lg2(g) = mltmod(a2w,lg2(g),m2)
      GO TO 50
 
   40 CALL xstopx ('ISDTYP NOT IN RANGE')
 
   50 cg1(g) = lg1(g)
      cg2(g) = lg2(g)
      RETURN
 
      END