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Diffstat (limited to 'Utilib/src/RANDD.f')
| -rw-r--r-- | Utilib/src/RANDD.f | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/Utilib/src/RANDD.f b/Utilib/src/RANDD.f new file mode 100644 index 0000000..c986f6c --- /dev/null +++ b/Utilib/src/RANDD.f @@ -0,0 +1,70 @@ +*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 |