| 1 | SUBROUTINE RNEGBI( N,XN,ECM )
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| 2 |
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| 3 | C-----------------------------------------------------------------------
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| 4 | C R(ANDOM NUMBER WITH) NEG(ATIVE) BI(NOMIAL DISTRIBUTION)
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| 5 | C
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| 6 | C RANDOM NUMBER GENERATOR FOR INTEGER NUMBERS DISTRIBUTED ACCORDING TO
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| 7 | C A NEGATIVE BINOMIAL DISTRIBUTION WITH PARAMETERS <N> AND K
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| 8 | C DELIVERS ONLY EVEN NUMBERS AS CHARGE MUST BE CONSERVED
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| 9 | C THIS SUBROUTINE IS CALLED FROM HDPM
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| 10 | C ARGUMENTS:
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| 11 | C XN = <N> AVERAGE VALUE OF N
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| 12 | C ECM = CENTER OF MASS ENERGY
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| 13 | C N = RANDOM NUMBER DISTRIBUTED WITH NEG. BIN. DISTR.
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| 14 | C-----------------------------------------------------------------------
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| 15 |
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| 16 | IMPLICIT NONE
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| 17 | *KEEP,RANDPA.
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| 18 | COMMON /RANDPA/ FAC,U1,U2,RD,NSEQ,ISEED,KNOR
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| 19 | DOUBLE PRECISION FAC,U1,U2
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| 20 | REAL RD(3000)
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| 21 | INTEGER ISEED(103,10),NSEQ
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| 22 | LOGICAL KNOR
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| 23 | *KEEP,RUNPAR.
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| 24 | COMMON /RUNPAR/ FIXHEI,THICK0,HILOECM,HILOELB,
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| 25 | * STEPFC,NRRUN,NSHOW,PATAPE,MONIIN,
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| 26 | * MONIOU,MDEBUG,NUCNUC,
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| 27 | * CETAPE,
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| 28 | * SHOWNO,ISHW,NOPART,NRECS,NBLKS,MAXPRT,NDEBDL,
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| 29 | * N1STTR,MDBASE,
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| 30 | * DEBDEL,DEBUG,FDECAY,FEGS,FIRSTI,FIXINC,FIXTAR,
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| 31 | * FIX1I,FMUADD,FNKG,FPRINT,FDBASE
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| 32 | * ,GHEISH,GHESIG
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| 33 | COMMON /RUNPAC/ DSN,HOST,USER
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| 34 | DOUBLE PRECISION FIXHEI,THICK0,HILOECM,HILOELB
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| 35 | REAL STEPFC
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| 36 | INTEGER NRRUN,NSHOW,PATAPE,MONIIN,MONIOU,MDEBUG,NUCNUC,
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| 37 | * SHOWNO,ISHW,NOPART,NRECS,NBLKS,MAXPRT,NDEBDL,
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| 38 | * N1STTR,MDBASE
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| 39 | INTEGER CETAPE
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| 40 | CHARACTER*79 DSN
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| 41 | CHARACTER*20 HOST,USER
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| 42 |
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| 43 | LOGICAL DEBDEL,DEBUG,FDECAY,FEGS,FIRSTI,FIXINC,FIXTAR,
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| 44 | * FIX1I,FMUADD,FNKG,FPRINT,FDBASE
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| 45 | * ,GHEISH,GHESIG
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| 46 | *KEND.
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| 47 |
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| 48 | DOUBLE PRECISION ECM,P,PN,Q,R,SUM,XI,XK,XN
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| 49 | INTEGER N
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| 50 | C-----------------------------------------------------------------------
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| 51 |
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| 52 | CC IF ( DEBUG ) WRITE(MDEBUG,*) 'RNEGBI: XN,ECM=',SNGL(XN),SNGL(ECM)
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| 53 |
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| 54 | C PARAMETRIZATION OF PARAMETER K OF NEG.BIN. DISTRIBUTION ACCORDING
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| 55 | C TO UA5 COLLABORATION, PHYS. LETT. 167B (1986) 476
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| 56 | XK = 1.D0 / ( -0.104D0 + 0.058D0 * LOG(ECM) )
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| 57 | C OTHER PARAMETERS
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| 58 | R = XN / XK
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| 59 | Q = 1.D0 / (1.D0 + R)
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| 60 | P = R * Q
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| 61 |
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| 62 | C VALUES FOR N EQUAL 0
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| 63 | 1 CONTINUE
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| 64 | N = 0
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| 65 | PN = Q**XK
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| 66 | SUM = PN
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| 67 | C GET UNIFORM RANDOM NUMBER
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| 68 | CALL RMMAR( RD,1,1 )
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| 69 | IF ( RD(1) .LE. SUM ) GOTO 100
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| 70 | C COMPARE WITH SUM OVER P(N)
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| 71 | DO 2 XI = 1.D0, 1350.D0
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| 72 | PN = PN * P * (XK - 1.D0 + XI) / XI
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| 73 | SUM = SUM + PN
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| 74 | IF ( RD(1) .LE. SUM ) THEN
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| 75 | N = XI
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| 76 | GOTO 100
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| 77 | ENDIF
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| 78 | 2 CONTINUE
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| 79 | N = 1350
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| 80 |
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| 81 | 100 CONTINUE
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| 82 | IF ( MOD(N,2) .NE. 0 .AND. N .NE. 1 ) GOTO 1
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| 83 | CC IF (DEBUG) WRITE(MDEBUG,*)'RNEGBI: RD(1),N,<N>=',RD(1),N,SNGL(XN)
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| 84 |
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| 85 | RETURN
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| 86 | END
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