#include "isajet/pilot.h"
      SUBROUTINE ISABEG(IFL)
C----------------------------------------------------------------------
C-
C-   Purpose and Methods : 
C-       Initialize a process before event generation
C-
C-   Created   5-FEB-1988   Serban D. Protopopescu
C-
C    Ver 7.14: Do logic after setting physics parameters
C----------------------------------------------------------------------
#if defined(CERNLIB_IMPNONE)
      IMPLICIT NONE
#endif
#include "isajet/nodcay.inc"
#include "isajet/idrun.inc"
#include "isajet/keys.inc"
#include "isajet/primar.inc"
#include "isajet/jetpar.inc"
#include "isajet/isloop.inc"
#include "isajet/xmssm.inc"
#include "isajet/isapw.inc"
C
      INTEGER IFL,I
      LOGICAL FIRST
      SAVE FIRST
      CHARACTER*30 ISAPW2
      SAVE ISAPW2
      DATA FIRST/.TRUE./
C          ISAPW2 is used to check whether ALDATA is loaded
      DATA ISAPW2/'ALDATA REQUIRED BY FORTRAN G,H'/
C
C          Initialize
C
      IF(ISAPW1.NE.ISAPW2) THEN
        PRINT*, ' ISABEG ERROR: BLOCK DATA ALDATA HAS NOT BEEN LOADED.'
        PRINT*, ' ISAJET CANNOT RUN WITHOUT IT.'
        PRINT*, ' PLEASE READ THE FINE MANUAL FOR ISAJET.'
        STOP99
      ENDIF
C
      IF (FIRST) THEN
        FIRST=.FALSE.
      ELSE
        CALL SETNXT
      ENDIF
      IEVT=0
      IEVGEN=0
      NEVENT=0
      IEVOL=1
      IFRG=1
C
C          Read in user data and decay table
C
      CALL READIN(IFL)
      IF(IFL.NE.0) GOTO 999
      CALL IDGEN
      IF(GOMSSM) THEN
        CALL DOMSSM
      ENDIF
      IF (KEYS(10).AND..NOT.GOMSSM) THEN
        CALL SETH
      END IF
      CALL SETDKY(.FALSE.)
C
C          Generate NSIGMA unevolved events for SIGF calculation
C
C          TWOJET events
      IF(KEYS(1)) THEN
        CALL MBSET
        CALL SETW
        CALL LOGIC
        CALL PRTLIM
        CALL PTFUN
        DO 105 I=1,NSIGMA
105     CALL TWOJET
        CALL TIMER(1)
C
C          E+E- events
      ELSE IF(KEYS(2)) THEN
        CALL SETW
        CALL LOGIC
        CALL PRTLIM
        CALL EEBEG
        CALL EEMAX
        DO 205 I=1,NSIGMA
205     CALL ELCTRN
        CALL TIMER(1)
C
C          DRELLYAN events
      ELSE IF(KEYS(3)) THEN
        CALL SETW
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL QFUNC
        DO 305 I=1,NSIGMA
305     CALL DRLLYN
        CALL TIMER(1)
C
C          MINBIAS events
      ELSE IF(KEYS(4)) THEN
        PBEAM(1)=HALFE
        PBEAM(2)=HALFE
        CALL PRTLIM
        CALL MBSET
        CALL TIMER(1)
C
C          SUPERSYM events
      ELSE IF(KEYS(5)) THEN
        CALL SETW
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL PTFUN
        DO 505 I=1,NSIGMA
505     CALL TWOJET
        CALL TIMER(1)
C
C          WPAIR events
      ELSE IF(KEYS(6)) THEN
        CALL SETW
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL PTFUN
        DO 605 I=1,NSIGMA
        CALL TWOJET
605     CALL WPAIR
        CALL TIMER(1)
C
C          HIGGS events
      ELSE IF(KEYS(7)) THEN
        CALL SETW
        IF(GOMSSM) THEN
          CALL SETHSS
        ELSE
          CALL SETH
        ENDIF
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL QFUNC
        DO 705 I=1,NSIGMA
705     CALL DRLLYN
        CALL TIMER(1)
C
C          PHOTON events
      ELSEIF(KEYS(8)) THEN
        CALL MBSET
        CALL SETW
        CALL LOGIC
        CALL PRTLIM
        CALL PTFUN
        DO 805 I=1,NSIGMA
805     CALL TWOJET
        CALL TIMER(1)
C
C          TCOLOR events
      ELSE IF(KEYS(9)) THEN
        CALL SETW
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL QFUNC
        DO 905 I=1,NSIGMA
905     CALL DRLLYN
        CALL TIMER(1)
C
C          WHIGGS events
      ELSE IF(KEYS(10)) THEN
        CALL SETW
        CALL MBSET
        CALL LOGIC
        CALL PRTLIM
        CALL PTFUN
        DO 906 I=1,NSIGMA
        CALL TWOJET
906     CALL WHIGGS
        CALL TIMER(1)
C
      ELSE
        STOP 99
      ENDIF
999   RETURN
      END