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diff --git a/Dragon/src/MCGSCA.f b/Dragon/src/MCGSCA.f
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+*DECK MCGSCA
+      SUBROUTINE MCGSCA(N,K,M,NOM,NZON,H,XST,B)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Calculate coefficients of a track for the characteristics integration.
+* Step-Characteristics scheme with tabulated exponential calls with
+* 'source term isolation' option turned on.
+*
+*Copyright:
+* Copyright (C) 2002 Ecole Polytechnique de Montreal
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version
+*
+*Author(s): R. Le Tellier
+*
+*Parameters: input
+* N       number of elements in the current track.
+* K       total number of volumes for which specific values
+*         of the neutron flux and reactions rates are required.
+* M       number of material mixtures.
+* NOM     vector containing the region number of the different segments
+*         of this track.
+* NZON    index-number of the mixture type assigned to each volume.
+* H       vector containing the lenght of the different segments of this
+*         track.
+* XST     macroscopic total cross section.
+*         and step characteristics (SC).
+*
+*Parameters: output
+* B       undefined.
+*
+*-----------------------------------------------------------------------
+*
+      IMPLICIT NONE
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER N,K,M,NOM(N),NZON(K)
+      REAL XST(0:M)
+      DOUBLE PRECISION H(N),B(N)
+*---
+* LOCAL VARIABLES
+*---
+      INTEGER I,NOMI,NZI
+      REAL TAU
+      DOUBLE PRECISION HID,TAUD
+*     tabulated exponential common block
+      REAL             E0, E1, PAS1, DX1, XLIM1
+      INTEGER          MEX1, LAU
+      PARAMETER      ( MEX1=7936 )
+      COMMON /EXP1/ E0(0:MEX1),E1(0:MEX1),PAS1,DX1,XLIM1
+*
+      DO I=2,N-1
+         NOMI=NOM(I)
+         NZI=NZON(NOMI)
+         HID=H(I)
+         TAUD=HID*XST(NZI)
+         TAU=REAL(TAUD)
+         IF(TAU.GE.XLIM1) THEN
+*        Out of the table range
+            B(I)=1.D0/XST(NZI)
+         ELSE
+*        Linear interpolation in table of (1-exp(-x))/x
+            LAU=INT(TAUD*PAS1)
+            B(I)=HID*(E0(LAU)+E1(LAU)*TAUD)
+         ENDIF
+      ENDDO
+*
+      RETURN
+      END