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[u/mrichter/AliRoot.git] / GEANT321 / erdecks / ertrnt.F

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+*
+* $Id$
+*
+* $Log$
+* Revision 1.1.1.1  1996/03/06 15:37:35  mclareni
+* Add geane321 source directories
+*
+*
+#include "geant321/pilot.h"
+*CMZ :  3.21/02 29/03/94  15.41.49  by  S.Giani
+*-- Author :
+      SUBROUTINE ERTRNT
+C.
+C.    ******************************************************************
+C.    *                                                                *
+C.    *    Average neutral track is extrapolated by one step           *
+C.    *                                                                *
+C.    *    ==>Called by : ERTRGO                                       *
+C.    *       Original routine : GTNINO                                *
+C.    *       Authors   M.Maire, E.Nagy  *********                     *
+C.    *                                                                *
+C.    ******************************************************************
+C.
+#include "geant321/ertrio.inc"
+#include "geant321/gconst.inc"
+#include "geant321/gctmed.inc"
+#include "geant321/gctrak.inc"
+*
+* *** Compute point where to store error matrix
+*
+      STEPER = BIG
+      DO 20 IPR = 1,NEPRED
+         STEPE  = BIG
+         IF (LELENG) STEPE = ERLENG(IPR) - SLENG
+         IF (LEPLAN) THEN
+            SCAL1 = 0.
+            SCAL2 = 0.
+            DO 18 I=1,3
+               SCAL1 = SCAL1 + ERPLO(I,4,IPR)*(ERPLO(I,3,IPR)-VECT(I))
+               SCAL2 = SCAL2 + ERPLO(I,4,IPR)*VECT(I+3)
+   18       CONTINUE
+            STEPE = SCAL1/SCAL2
+         ENDIF
+         IF (STEPE.LE.PREC) STEPE = BIG
+         IF (STEPE.LT.STEPER) THEN
+            STEPER = STEPE
+            INLIST = IPR
+         ENDIF
+   20 CONTINUE
+*
+      STEP = BIG
+      CALL GTNEXT
+*
+      IF(STEPER.LT.SNEXT) THEN
+         STEP = STEPER
+         INWVOL = 0
+         IMEC   = 27
+         NMEC   = NMEC + 1
+         LMEC(NMEC) = IMEC
+      ELSE
+         STEP = SNEXT + PREC
+         INWVOL = 2
+         IMEC   = 1
+         NMEC   = NMEC + 1
+         LMEC(NMEC) = IMEC
+         IF ((STEPER-SNEXT).LE.(2*PREC)) THEN
+            IMEC   = 27
+            NMEC   = NMEC + 1
+            LMEC(NMEC) = IMEC
+         ENDIF
+      ENDIF
+*
+* *** Linear transport
+*
+      DO 25 I=1,3
+         VECT(I) = VECT(I) + STEP*VECT(I+3)
+   25 CONTINUE
+*
+      SLENG = SLENG + STEP
+*
+* *** Propagate error matrix
+*
+      IF (.NOT. LEONLY) CALL ERPROP
+*
+* *** Store informations
+*
+      IF(IMEC.EQ.27) CALL ERSTOR
+*
+      END