| fe4da5cc |
1 | * |
| 2 | * $Id$ |
| 3 | * |
| 4 | * $Log$ |
| 5 | * Revision 1.1.1.1 1995/10/24 10:19:54 cernlib |
| 6 | * Geant |
| 7 | * |
| 8 | * |
| 9 | #include "geant321/pilot.h" |
| 10 | *CMZ : 3.21/02 29/03/94 15.41.41 by S.Giani |
| 11 | *-- Author : |
| 12 | *$ CREATE BETRST.FOR |
| 13 | *COPY BETRST |
| 14 | * |
| 15 | *=== betrst ===========================================================* |
| 16 | * |
| 17 | FUNCTION BETRST ( GAM, ETA, X0, X1 ) |
| 18 | |
| 19 | #include "geant321/dblprc.inc" |
| 20 | #include "geant321/dimpar.inc" |
| 21 | #include "geant321/iounit.inc" |
| 22 | * |
| 23 | *----------------------------------------------------------------------* |
| 24 | * * |
| 25 | * New version: * |
| 26 | * Created on 20 february 1991 by Alfredo Ferrari & Paola Sala * |
| 27 | * Infn - Milan * |
| 28 | * * |
| 29 | * Last change on 20-feb-91 by Alfredo Ferrari * |
| 30 | * * |
| 31 | * Sampling from beta distribution in [X0,X1) : * |
| 32 | * * |
| 33 | * P(X) = X**(GAM-1.D0)*(1.D0-X)**(ETA-1)*GAMM(ETA+GAM) * |
| 34 | * / (GAMM(GAM*GAMM(ETA)) * |
| 35 | * * |
| 36 | *----------------------------------------------------------------------* |
| 37 | * |
| 38 | REAL RNDM(2) |
| 39 | * |
| 40 | * +-------------------------------------------------------------------* |
| 41 | * | |
| 42 | IF ( X1 .LT. X0 ) THEN |
| 43 | WRITE (LUNOUT,*)' Betrst: x1<x0, gam, eta', X1, X0, GAM, ETA |
| 44 | WRITE (LUNERR,*)' Betrst: x1<x0, gam, eta', X1, X0, GAM, ETA |
| 45 | X0 = MIN ( X0, ONEONE-0.05 ) |
| 46 | X1 = MIN ( ONEONE, X0/TWOTHI ) |
| 47 | END IF |
| 48 | * | |
| 49 | * +-------------------------------------------------------------------* |
| 50 | GAMI = 1.D+00 / GAM |
| 51 | X0GAM = X0**GAM |
| 52 | X1GAM = X1**GAM |
| 53 | X0TO1 = 1.D+00 - X0 |
| 54 | CNORM = X1GAM - X0GAM |
| 55 | ETAM1 = ETA - 1.D+00 |
| 56 | NTAM1 = NINT (ETA - 1.D+00) |
| 57 | * +-------------------------------------------------------------------* |
| 58 | * | |
| 59 | IF ( ETAM1 - NTAM1 .NE. 0.D+00 ) THEN |
| 60 | * | +----------------------------------------------------------------* |
| 61 | * | | First sample from X**(gam-1) and then reject according to |
| 62 | * | | (1-X)**(eta-1) |
| 63 | 100 CONTINUE |
| 64 | CALL GRNDM(RNDM,2) |
| 65 | BETRST = ( RNDM (1) * CNORM + X0GAM )**GAMI |
| 66 | REJE = ( ( 1.D+00 - BETRST ) / X0TO1 )**ETAM1 |
| 67 | IF ( RNDM (2) .GE. REJE ) GO TO 100 |
| 68 | * | | |
| 69 | * | +----------------------------------------------------------------* |
| 70 | * | |
| 71 | * +-------------------------------------------------------------------* |
| 72 | * | |
| 73 | ELSE |
| 74 | * | +----------------------------------------------------------------* |
| 75 | * | | First sample from X**(gam-1) and then reject according to |
| 76 | * | | (1-X)**(eta-1) |
| 77 | 200 CONTINUE |
| 78 | CALL GRNDM(RNDM,2) |
| 79 | BETRST = ( RNDM (1) * CNORM + X0GAM )**GAMI |
| 80 | REJE = ( ( 1.D+00 - BETRST ) / X0TO1 )**NTAM1 |
| 81 | IF ( RNDM (2) .GE. REJE ) GO TO 200 |
| 82 | * | | |
| 83 | * | +----------------------------------------------------------------* |
| 84 | END IF |
| 85 | * | |
| 86 | * +-------------------------------------------------------------------* |
| 87 | RETURN |
| 88 | *=== End of function betrst ===========================================* |
| 89 | END |
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