! $Id: ran1.f90 5105 2024-07-23 17:14:34Z abarral $

FUNCTION RAN1(IDUM)
  IMPLICIT NONE
  REAL :: RAN1
  REAL,SAVE :: R(97)
  REAL,PARAMETER :: RM1=3.8580247E-6,RM2=7.4373773E-6
  INTEGER,SAVE :: IFF=0
  integer,save :: ix1,ix2,ix3
  INTEGER,PARAMETER :: M1=259200,IA1=7141,IC1=54773
  INTEGER,PARAMETER :: M2=134456,IA2=8121,IC2=28411
  INTEGER,PARAMETER :: M3=243000,IA3=4561,IC3=51349
  INTEGER :: IDUM,J

  IF (IDUM<0.OR.IFF==0) THEN
    IFF=1
    IX1=MOD(IC1-IDUM,M1)
    IX1=MOD(IA1*IX1+IC1,M1)
    IX2=MOD(IX1,M2)
    IX1=MOD(IA1*IX1+IC1,M1)
    IX3=MOD(IX1,M3)
    DO J=1,97
      IX1=MOD(IA1*IX1+IC1,M1)
      IX2=MOD(IA2*IX2+IC2,M2)
      R(J)=(REAL(IX1)+REAL(IX2)*RM2)*RM1
  END DO
    IDUM=1
  ENDIF
  IX1=MOD(IA1*IX1+IC1,M1)
  IX2=MOD(IA2*IX2+IC2,M2)
  IX3=MOD(IA3*IX3+IC3,M3)
  J=1+(97*IX3)/M3
  IF(J>97.OR.J<1) stop 1
  RAN1=R(J)
  R(J)=(REAL(IX1)+REAL(IX2)*RM2)*RM1

END FUNCTION RAN1