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

---
 Utilib/src/ALLUS.f | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 Utilib/src/ALLUS.f

(limited to 'Utilib/src/ALLUS.f')

diff --git a/Utilib/src/ALLUS.f b/Utilib/src/ALLUS.f
new file mode 100644
index 0000000..0d4926a
--- /dev/null
+++ b/Utilib/src/ALLUS.f
@@ -0,0 +1,62 @@
+*DECK ALLUS
+      SUBROUTINE ALLUS(L4,MU1,IMA,ASS,F)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* solution of a linear system where the coefficient matrix have been
+* factorized by a preceding call to ALLUF.
+*
+*Copyright:
+* Copyright (C) 1989 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
+* L4      order of the coefficient matrix.
+* MU1     position of each diagonal element in vector ASS.
+* IMA     position of the first non-zero column element in vector ASS.
+* ASS     LU factors of the coefficient matrix in compressed diagonal
+*         storage mode. DIMENSION ASS(IMA(L4))
+* F       right-hand side of the linear system.
+*
+*Parameters: output
+* F       solution of the linear system.
+*
+*-----------------------------------------------------------------------
+*
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER L4,MU1(L4),IMA(L4)
+      REAL ASS(*),F(L4)
+*
+      F(1)=F(1)/ASS(MU1(1))
+      DO 20 I=2,L4
+      K1=IMA(I-1)+1
+      K2=MU1(I)
+      KJ=I-K2+K1
+      T=-F(I)
+      DO 10 K=K1,K2-1
+      T=T+F(KJ)*ASS(K)
+      KJ=KJ+1
+   10 CONTINUE
+      F(I)=-T/ASS(MU1(I))
+   20 CONTINUE
+*
+      DO 40 I=L4,2,-1
+      K1=IMA(I)
+      K2=MU1(I)
+      KJ=I-K1+K2
+      T=-F(I)
+      DO 30 K=K1,K2+1,-1
+      F(KJ)=F(KJ)+ASS(K)*T
+      KJ=KJ+1
+   30 CONTINUE
+   40 CONTINUE
+      RETURN
+      END
-- 
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