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Commit | Line | Data |
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fe4da5cc | 1 | * |
2 | * $Id$ | |
3 | * | |
4 | * $Log$ | |
5 | * Revision 1.1.1.1 1996/04/01 15:02:55 mclareni | |
6 | * Mathlib gen | |
7 | * | |
8 | * | |
9 | #include "gen/pilot.h" | |
10 | FUNCTION RANGAM(P) | |
11 | C THIS FUNCTION GENERATES A GAMMA DISTRIBUTED RANDOM NUMBER | |
12 | C WITH PARAMETER P .GT.0. | |
13 | C THE JOHNK S ALGORITHM IS USED | |
14 | DIMENSION STOR(20) | |
15 | RANGAM=0. | |
16 | IF(P.GT.15.) GO TO 40 | |
17 | M=INT(P) | |
18 | F=P-M | |
19 | IF(M.EQ.0) GO TO 20 | |
20 | X=1. | |
21 | CALL NRAN(STOR,M) | |
22 | DO 1 I=1,M | |
23 | 1 X = X * STOR(I) | |
24 | RANGAM=-LOG(X) | |
25 | 20 IF ( F .LT. 1.0E-5) RETURN | |
26 | C | |
27 | X1=-LOG(RNDM(3)) | |
28 | IF (F .LT. 0.9999) GO TO 25 | |
29 | 22 RANGAM = RANGAM + X1 | |
30 | RETURN | |
31 | C NON-INTEGER VALUE OF P | |
32 | 25 CONTINUE | |
33 | C ....W1=R1**(1/F) | |
34 | WLOG = LOG (RNDM (1) ) / F | |
35 | IF (WLOG .LT. -100.) RETURN | |
36 | W1 = EXP(WLOG) | |
37 | C ....W2=R2**(1/(1-F)) | |
38 | WLOG = LOG(RNDM(2)) / (1.-F) | |
39 | IF (WLOG .LT. -100.) GO TO 22 | |
40 | W2 = EXP(WLOG) | |
41 | W=W1+W2 | |
42 | IF(W.GT.1.) GO TO 25 | |
43 | X2=W1/W | |
44 | RANGAM=RANGAM+X1*X2 | |
45 | RETURN | |
46 | C | |
47 | C WILSON - HILFERTY APPROXIMATION | |
48 | #if (defined(CERNLIB_IBM)||defined(CERNLIB_CDC))&&(!defined(CERNLIB_FORTRAN)) | |
49 | 40 CALL NORRAN(A) | |
50 | #endif | |
51 | #if (!defined(CERNLIB_IBM)||defined(CERNLIB_FORTRAN))&&(!defined(CERNLIB_CDC)||defined(CERNLIB_FORTRAN)) | |
52 | 40 CALL RANNOR(A,B) | |
53 | #endif | |
54 | Q=1.-1./(9.*P)+A/(3.*SQRT(P)) | |
55 | RANGAM=P*Q*Q*Q | |
56 | IF (RANGAM.LE.0.) GO TO 40 | |
57 | RETURN | |
58 | END |