This commit was generated by cvs2svn to compensate for changes in r2,

[u/mrichter/AliRoot.git] / GEANT321 / gstrag / gstren.F

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+*
+* $Id$
+*
+* $Log$
+* Revision 1.1.1.1  1995/10/24 10:21:39  cernlib
+* Geant
+*
+*
+#include "geant321/pilot.h"
+*CMZ :  3.21/02 29/03/94  15.41.25  by  S.Giani
+*-- Author :
+      FUNCTION GSTREN (GAMMA,ECUT,STEP)
+C.    ******************************************************************
+C.    *                                                                *
+C.    *   Simulation of energy loss straggling in thin layers.         *
+C.    *   Sampling is done from the tables which are prepared          *
+C.    *   in GSTINI.                                                   *
+C.    *                                                                *
+C.    *   ==> Called by : GTELEC, GTHADR, GTMUON                       *
+C.    *       Authors   : K. Lassila-Perini, I. Gavrilenko             *
+C.    *                                                                *
+C.    ******************************************************************
+#include "geant321/gcbank.inc"
+#include "geant321/gcjloc.inc"
+#include "geant321/gcmate.inc"
+#include "geant321/gcstra.inc"
+C
+      DIMENSION ANGL(200),RNDM(2)
+C...
+*   Reading the tables, if the medium has not changed
+      NP     = Q(JTSTRA+1)
+*
+      EC       = 1.E9*ECUT
+      GSTLOC   = 0.
+      IF(STEP.LE.0.) GO TO 90
+C...
+*   Interpolate the tables for the current gamma-factor
+      GAML     = LOG(GAMMA)
+      IF(GAML.GT.GAMLOG(21)) THEN
+         DO 10 J=1,NP
+            ANGL(J)=Q(JTSTCO+J*21)
+   10    CONTINUE
+      ELSE
+C...
+         DO 20 I = 2,21
+            IF(GAML.LE.GAMLOG(I)) THEN
+               DGG = (GAML-GAMLOG(I-1))/(GAMLOG(I)-GAMLOG(I-1))
+               IP=I
+               GO TO 30
+            ENDIF
+   20    CONTINUE
+   30    DG1=1.-DGG
+C...
+         DO 40 K = 1,NP
+            ANGL(K) = Q(JTSTCO+(K-1)*21+IP-1)*DG1+
+     +                Q(JTSTCO+(K-1)*21+IP  )*DGG
+   40    CONTINUE
+      ENDIF
+*
+*    The sampling from the tables
+      ANMIN   = EXP(ANGL(NP))
+      ANMAX   = EXP(ANGL( 1))
+*
+      DAN      = ANMAX-ANMIN
+      AMU      = DAN*STEP
+      CALL GPOISS(AMU,N,1)
+      NICOLL   = MAX(N,1)
+      DO 80  I  = 1,NICOLL
+   50    K1 = 1
+         K2 = NP
+         CALL GRNDM(RNDM,1)
+         R = LOG(RNDM(1)*DAN+ANMIN)
+   60    K = (K1+K2)/2
+         IF(R.GT.ANGL(K)) THEN
+            K2=K
+         ELSEIF(R.LT.ANGL(K)) THEN
+            K1=K
+         ELSE
+            E=Q(JTSTEN+K)
+            GOTO 70
+         ENDIF
+         IF(K2-K1.GT.1 ) GO TO 60
+*
+         E = Q(JTSTEN+K2)+(R-ANGL(K2))*
+     +       (Q(JTSTEN+K1)-Q(JTSTEN+K2))/(ANGL(K1)-ANGL(K2))
+   70    EE = EXP(E)
+         IF(EE.GT.EC) GO TO 50
+*
+* *** Total energy calculation
+         GSTLOC = GSTLOC+EE
+   80 CONTINUE
+*
+   90 GSTREN  = GSTLOC*1.E-9
+      END