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diff --git a/Dragon/src/MCGDDF.f b/Dragon/src/MCGDDF.f
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+*DECK MCGDDF
+      SUBROUTINE MCGDDF(N,K,M,NOM,NZON,H,XST,B)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Calculate coefficients of a track for the characteristics integration.
+* Diamond-Differencing scheme without fix-up 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.
+*
+*Parameters: output
+* B       DD1 coefficients.
+*
+*-----------------------------------------------------------------------
+*
+      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
+      DOUBLE PRECISION TAUD,HID
+*
+      DO I=2,N-1
+         NOMI=NOM(I)
+         NZI=NZON(NOMI)
+         HID=H(I)
+         TAUD=HID*XST(NZI)
+         B(I)=2.D0*HID/(2.D0+TAUD)
+      ENDDO
+*
+      RETURN
+      END