*
* $Id: gpgaus.F,v 3.1.1.1 2002/07/11 16:02:00 cafagna Exp $
*
* $Log: gpgaus.F,v $
* Revision 3.1.1.1  2002/07/11 16:02:00  cafagna
* First GPAMELA release on CVS
*
*
*CMZ :  2.01/00 05/04/2000  14.35.18  by  Marialuigia Ambriola
*CMZ :  2.00/00 03/03/2000  15.39.05  by  Francesco Cafagna
*CMZ :  1.01/00 06/05/96  12.57.18  by  Francesco Cafagna
*-- Author :    Francesco Cafagna   03/05/96
      REAL FUNCTION GPGAUS(XDUMMY)
************************************************************************
*                                                                      *
* To generate a normally distribute deviate with zero mean and unit variance *
* From GASDEV, Numerical recepies $7.3.                                *
* Variables definition:                                                *
* IN:                                                                  *
*  XDUMMY, dummy argument                                              *
*                                                                      *
* Called by:<USER>                                                     *
* Author: Francesco Cafagna, 03/05/96 17.11.14                         *
*                                                                      *
************************************************************************
      INTEGER ISET
      REAL V1,V2,GAS1,RVAL(2),R
*
      DATA ISET/0/
*
* Generate a random number in the circle of radius 1
*
      IF (ISET.EQ.0) THEN
   10    CALL GRNDM(RVAL,2)
         V1 = 2.*RVAL(1) -1.
         V2 = 2.*RVAL(2) -1.
         R  = V1**2 + V2**2
         IF(R.GE.1.) GO TO 10
         GAS1 = V1 * SQRT(-2.*LOG(R)/R)
         GPGAUS = V2 * SQRT(-2.*LOG(R)/R)
         ISET = 1
      ELSE
         GPGAUS = GAS1
         ISET = 0
      ENDIF
*
      RETURN
      END