From 7dfcc480ba1e19bd3232349fc733caef94034292 Mon Sep 17 00:00:00 2001
From: stainer_t <thomas.stainer@oecd-nea.org>
Date: Mon, 8 Sep 2025 13:48:49 +0200
Subject: Initial commit from Polytechnique Montreal

---
 Dragon/src/MCGSCES.f | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 Dragon/src/MCGSCES.f

(limited to 'Dragon/src/MCGSCES.f')

diff --git a/Dragon/src/MCGSCES.f b/Dragon/src/MCGSCES.f
new file mode 100644
index 0000000..7b70242
--- /dev/null
+++ b/Dragon/src/MCGSCES.f
@@ -0,0 +1,78 @@
+*DECK MCGSCES
+      SUBROUTINE MCGSCES(N,K,M,NOM,NZON,H,XST,B)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Calculate coefficients of a track for the characteristics integration.
+* Step-Characteristics scheme with exact exponential calls with
+* 'source term isolation' option turned off.
+*
+*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       undefined.
+*
+*-----------------------------------------------------------------------
+*
+      IMPLICIT NONE
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER N,K,M,NOM(N),NZON(K)
+      REAL XST(0:M)
+      DOUBLE PRECISION H(N),B(2,N)
+*---
+* LOCAL VARIABLES
+*---
+      INTEGER I,NOMI,NZI
+      DOUBLE PRECISION TAUDMIN,TAUD,HID,HID2,TAUD3,TAUD4,TAUD5
+*     tabulated exponential common block
+      REAL             E0, E1, PAS1, DX1, XLIM1
+      INTEGER          MEX1, LAU
+      PARAMETER      ( MEX1=7936, TAUDMIN=2.D-2 )
+      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)
+         IF(TAUD.LE.TAUDMIN) THEN  
+*        Linear interpolation in table of (1-exp(-x))/x
+            LAU=INT(TAUD*PAS1)
+            B(1,I)=HID*(E0(LAU)+E1(LAU)*TAUD)
+*           and expansion in Taylor serie in O(TAUD^3)
+            TAUD3=TAUD/3.D0
+            TAUD4=0.125D0*TAUD
+            TAUD5=0.2D0*TAUD
+            HID2=HID*HID
+            B(2,I)=HID2*(0.5D0-TAUD3*(0.5D0-TAUD4*(1.D0-TAUD5)))
+         ELSE
+*        Exact exponential
+            B(1,I)=(1.D0-DEXP(-TAUD))/XST(NZI)
+            B(2,I)=(HID-B(1,I))/XST(NZI)
+         ENDIF
+      ENDDO
+*
+      RETURN
+      END
-- 
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