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/SYB41C.f | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 Dragon/src/SYB41C.f

(limited to 'Dragon/src/SYB41C.f')

diff --git a/Dragon/src/SYB41C.f b/Dragon/src/SYB41C.f
new file mode 100644
index 0000000..d87177a
--- /dev/null
+++ b/Dragon/src/SYB41C.f
@@ -0,0 +1,72 @@
+*DECK SYB41C
+      SUBROUTINE SYB41C(PP,TAU0,TAUI,TAUJ)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Evaluation of the $C_{ij}$ function in 1D spherical geometry.
+*
+*Copyright:
+* Copyright (C) 2005 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): A. Hebert
+*
+*Parameters: input
+* TAU0   side to side optical path.
+* TAUI   optical path in volume i (or volume j).
+* TAUJ   optical path in volume j (or volume i).
+*
+*Parameters: output
+* PP   value of the expression.
+*
+*-----------------------------------------------------------------------
+*
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      REAL PP,TAU0,TAUI,TAUJ
+*----
+*  SYMMETRIC FORMULA IN (I,J). WE SET POPI <= POPJ
+*----
+      IF(TAUJ.LT.TAUI) THEN
+         POPI = TAUJ
+         POPJ = TAUI
+      ELSE
+         POPI = TAUI
+         POPJ = TAUJ
+      ENDIF
+      IF(POPI.GT.0.004) THEN
+         PP=EXP(-TAU0)-EXP(-(TAU0+POPI))-EXP(-(TAU0+POPJ))+
+     1      EXP(-(TAU0+POPI+POPJ))
+      ELSE IF((POPI.GT.0.002).AND.(POPJ.GT.0.004)) THEN
+         PP=EXP(-TAU0)-EXP(-(TAU0+POPI))-EXP(-(TAU0+POPJ))+
+     1      EXP(-(TAU0+POPI+POPJ))
+         PQ=POPI*(EXP(-TAU0)-EXP(-(TAU0+POPJ)))
+         FACTI=500.0*(POPI-0.002)
+         PP=PP*FACTI+PQ*(1.0-FACTI)
+      ELSE IF((POPI.GT.0.002).AND.(POPJ.GT.0.002)) THEN
+         PP=EXP(-TAU0)-EXP(-(TAU0+POPI))-EXP(-(TAU0+POPJ))+
+     1      EXP(-(TAU0+POPI+POPJ))
+         PQ=POPI*(EXP(-TAU0)-EXP(-(TAU0+POPJ)))
+         PR=POPJ*(EXP(-TAU0)-EXP(-(TAU0+POPI)))
+         PS=POPI*POPJ*EXP(-TAU0)
+         FACTI=500.0*(POPI-0.002)
+         FACTJ=500.0*(POPJ-0.002)
+         PP=PP*FACTI*FACTJ+PQ*(1.0-FACTI)*FACTJ+PR*FACTI*(1.0-FACTJ)
+     1     +PS*(1.0-FACTI)*(1.0-FACTJ)
+      ELSE IF(POPJ.GT.0.004) THEN
+         PP=POPI*(EXP(-TAU0)-EXP(-(TAU0+POPJ)))
+      ELSE IF(POPJ.GT.0.002) THEN
+         PP=POPI*(EXP(-TAU0)-EXP(-(TAU0+POPJ)))
+         PS=POPI*POPJ*EXP(-TAU0)
+         FACTJ=500.0*(POPJ-0.002)
+         PP=PP*FACTJ+PS*(1.0-FACTJ)
+      ELSE
+         PP=POPI*POPJ*EXP(-TAU0)
+      ENDIF
+      RETURN
+      END
-- 
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