[u/mrichter/AliRoot.git] / GEANT321 / gphys / gpoiss.F

*
* $Id$
*
* $Log$
* Revision 1.1.1.1  1995/10/24 10:21:32  cernlib
* Geant
*
*
#include "geant321/pilot.h"
*CMZ :  3.21/02 29/03/94  15.41.23  by  S.Giani
*-- Author :
      SUBROUTINE GPOISS(AMVEC,NPVEC,LEN)
C.
C.    ******************************************************************
C.    *                                                                *
C.    *  Generates  a vector NPVEC of LEN random numbers               *
C.    *  POISSON distribued with mean values AMVEC                     *
C.    *                                                                *
C.    *  If the mean value A greater than PLIM, N is calculated        *
C.    *  according to the Gaussian approximation of the Poisson        *
C.    *  distribution.                                                 *
C.    *                                                                *
C.    *     ==> Called by : GLANDZ,GMCOUL                              *
C.    *                                                                *
C.    *  Author      : L.Urban                                         *
C.    *  Date        : 28.04.1988           Last update :  1.02.1990   *
C.    *                                                                *
C.    ******************************************************************
C.
#include "geant321/gconsp.inc"
      REAL AMVEC(*),RNDM(2), N
      INTEGER NPVEC(*)
      PARAMETER (PLIM=16.,HMXINT=2E+9)
*
      DO 30 I=1,LEN
*     Protection against negative mean values
         N=0.
         IF(AMVEC(I).GT.0.) THEN
            IF(AMVEC(I).LE.PLIM) THEN
               CALL GRNDM(RNDM,1)
               R=RNDM(1)
               P=EXP(-AMVEC(I))
               S=P
               IF(R.LE.S) GOTO 20
   10          N=N+1.
               P=P*AMVEC(I)/N
               S=S+P
               IF(S.LT.R.AND.P.GT.1.E-30) GOTO 10
            ELSE
               CALL GRNDM(RNDM,2)
               RR=SQRT(-2.*LOG(RNDM(1)))
               PHI=TWOPI*RNDM(2)
               X=RR*COS(PHI)
               N=MIN(MAX(AMVEC(I)+X*SQRT(AMVEC(I)),0.),HMXINT)
            ENDIF
         ENDIF
*
   20    NPVEC(I) = N
   30 CONTINUE
*
      END
Commit	Line	Data
fe4da5cc	1	*
	2	* $Id$
	3	*
	4	* $Log$
	5	* Revision 1.1.1.1 1995/10/24 10:21:32 cernlib
	6	* Geant
	7	*
	8	*
	9	#include "geant321/pilot.h"
	10	*CMZ : 3.21/02 29/03/94 15.41.23 by S.Giani
	11	*-- Author :
	12	SUBROUTINE GPOISS(AMVEC,NPVEC,LEN)
	13	C.
	14	C. ******************************************************************
	15	C. * *
	16	C. * Generates a vector NPVEC of LEN random numbers *
	17	C. * POISSON distribued with mean values AMVEC *
	18	C. * *
	19	C. * If the mean value A greater than PLIM, N is calculated *
	20	C. * according to the Gaussian approximation of the Poisson *
	21	C. * distribution. *
	22	C. * *
	23	C. * ==> Called by : GLANDZ,GMCOUL *
	24	C. * *
	25	C. * Author : L.Urban *
	26	C. * Date : 28.04.1988 Last update : 1.02.1990 *
	27	C. * *
	28	C. ******************************************************************
	29	C.
	30	#include "geant321/gconsp.inc"
	31	REAL AMVEC(*),RNDM(2), N
	32	INTEGER NPVEC(*)
	33	PARAMETER (PLIM=16.,HMXINT=2E+9)
	34	*
	35	DO 30 I=1,LEN
	36	* Protection against negative mean values
	37	N=0.
	38	IF(AMVEC(I).GT.0.) THEN
	39	IF(AMVEC(I).LE.PLIM) THEN
	40	CALL GRNDM(RNDM,1)
	41	R=RNDM(1)
	42	P=EXP(-AMVEC(I))
	43	S=P
	44	IF(R.LE.S) GOTO 20
	45	10 N=N+1.
	46	P=P*AMVEC(I)/N
	47	S=S+P
	48	IF(S.LT.R.AND.P.GT.1.E-30) GOTO 10
	49	ELSE
	50	CALL GRNDM(RNDM,2)
	51	RR=SQRT(-2.*LOG(RNDM(1)))
	52	PHI=TWOPI*RNDM(2)
	53	X=RR*COS(PHI)
	54	N=MIN(MAX(AMVEC(I)+X*SQRT(AMVEC(I)),0.),HMXINT)
	55	ENDIF
	56	ENDIF
	57	*
	58	20 NPVEC(I) = N
	59	30 CONTINUE
	60	*
	61	END