PYTHIA/jetset/rlu.F

   1
   2 C*********************************************************************
   3
   4       FUNCTION RLU(IDUMMY)
   5
   6 C...Purpose: to generate random numbers uniformly distributed between
   7 C...0 and 1, excluding the endpoints.
   8       COMMON/LUDATR/MRLU(6),RRLU(100)
   9       SAVE /LUDATR/
  10       EQUIVALENCE (MRLU1,MRLU(1)),(MRLU2,MRLU(2)),(MRLU3,MRLU(3)),
  11      &(MRLU4,MRLU(4)),(MRLU5,MRLU(5)),(MRLU6,MRLU(6)),
  12      &(RRLU98,RRLU(98)),(RRLU99,RRLU(99)),(RRLU00,RRLU(100))
  13
  14 C...Initialize generation from given seed.
  15       IF(MRLU2.EQ.0) THEN
  16         IJ=MOD(MRLU1/30082,31329)
  17         KL=MOD(MRLU1,30082)
  18         I=MOD(IJ/177,177)+2
  19         J=MOD(IJ,177)+2
  20         K=MOD(KL/169,178)+1
  21         L=MOD(KL,169)
  22         DO 110 II=1,97
  23         S=0.
  24         T=0.5
  25         DO 100 JJ=1,24
  26         M=MOD(MOD(I*J,179)*K,179)
  27         I=J
  28         J=K
  29         K=M
  30         L=MOD(53*L+1,169)
  31         IF(MOD(L*M,64).GE.32) S=S+T
  32         T=0.5*T
  33   100   CONTINUE
  34         RRLU(II)=S
  35   110   CONTINUE
  36         TWOM24=1.
  37         DO 120 I24=1,24
  38         TWOM24=0.5*TWOM24
  39   120   CONTINUE
  40         RRLU98=362436.*TWOM24
  41         RRLU99=7654321.*TWOM24
  42         RRLU00=16777213.*TWOM24
  43         MRLU2=1
  44         MRLU3=0
  45         MRLU4=97
  46         MRLU5=33
  47       ENDIF
  48
  49 C...Generate next random number.
  50   130 RUNI=RRLU(MRLU4)-RRLU(MRLU5)
  51       IF(RUNI.LT.0.) RUNI=RUNI+1.
  52       RRLU(MRLU4)=RUNI
  53       MRLU4=MRLU4-1
  54       IF(MRLU4.EQ.0) MRLU4=97
  55       MRLU5=MRLU5-1
  56       IF(MRLU5.EQ.0) MRLU5=97
  57       RRLU98=RRLU98-RRLU99
  58       IF(RRLU98.LT.0.) RRLU98=RRLU98+RRLU00
  59       RUNI=RUNI-RRLU98
  60       IF(RUNI.LT.0.) RUNI=RUNI+1.
  61       IF(RUNI.LE.0.OR.RUNI.GE.1.) GOTO 130
  62
  63 C...Update counters. Random number to output.
  64       MRLU3=MRLU3+1
  65       IF(MRLU3.EQ.1000000000) THEN
  66         MRLU2=MRLU2+1
  67         MRLU3=0
  68       ENDIF
  69       RLU=RUNI
  70
  71       RETURN
  72       END