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*DECK RANDD
SUBROUTINE RANDD(ISEED,NRAND,DRAND)
*
*-----------------------------------------------------------------------
*
*Purpose:
* This subroutine returns a pseudo-random number for each invocation.
* It is a FORTRAN 77 adaptation of the "Integer Version 2" minimal
* standard number generator whose Pascal code appears in reference.
* This is the double precision version of the single precision
* routine RANDF.
*
*
*Copyright:
* Copyright (C) 2008 Ecole Polytechnique de Montreal
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version
*
*Author(s): R. Chambon
*
*Parameters: input
* ISEED the seed for the generation of random numbers. If ISEED=0
* use ISEED=3141592654
* NRAND number of random number requested.
*
*Parameters: ouput
* DRAND random numbers between 0 and 1.
*
*Reference:
* Park, Steven K. and Miller, Keith W., "Random Number Generators:
* Good Ones are Hard to Find", Communications of the ACM, October 1988.
*
*-----------------------------------------------------------------------
*
IMPLICIT NONE
*----
* SUBROUTINE ARGUMENTS
*----
INTEGER ISEED,NRAND
DOUBLE PRECISION DRAND(NRAND)
*----
* LOCAL VARIABLES
*----
INTEGER MPLIER,MODLUS,MOBYMP,MOMDMP
PARAMETER (MPLIER=16807,MODLUS=2147483647,MOBYMP=127773,
+ MOMDMP=2836)
INTEGER IRAND,HVLUE,LVLUE,TESTV,NEXTN
*
IF(ISEED .EQ. 0) THEN
NEXTN = 314159265
ELSE
NEXTN = ISEED
ENDIF
*
DO IRAND=1,NRAND
HVLUE = NEXTN / MOBYMP
LVLUE = MOD(NEXTN, MOBYMP)
TESTV = MPLIER*LVLUE - MOMDMP*HVLUE
IF (TESTV .GT. 0) THEN
NEXTN = TESTV
ELSE
NEXTN = TESTV + MODLUS
ENDIF
DRAND(IRAND) = DBLE(NEXTN)/DBLE(MODLUS)
ENDDO
ISEED= NEXTN
RETURN
END
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