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/ALVDLS.f | 143 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 Utilib/src/ALVDLS.f

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

diff --git a/Utilib/src/ALVDLS.f b/Utilib/src/ALVDLS.f
new file mode 100644
index 0000000..3c35a72
--- /dev/null
+++ b/Utilib/src/ALVDLS.f
@@ -0,0 +1,143 @@
+*DECK ALVDLS
+      SUBROUTINE ALVDLS (LTSW,MU1,ASS,F,ISEG,LON,NBL,LBL)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* solution of a symmetric linear system where the coefficient matrix
+* have been previously factorized as LDL(T). Supervectorial version.
+*
+*Copyright:
+* Copyright (C) 1992 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
+* LTSW    maximum bandwidth. =2 for tridiagonal systems.
+* MU1     position of each diagonal element in vector ass.
+*         DIMENSION MU1(L4) where L4=SUM(LBL(I))
+* ASS     LDL(T) factors of the coefficient matrix in compressed
+*         diagonal storage mode. DIMENSION ASS(ISEG,MU1(L4))
+* F       right-hand side of the linear system. DIMENSION F(ISEG,L4)
+* ISEG    number of elements in a vector register.
+* LON     number of groups of linear systems.
+* NBL     number of linear systems in each group. DIMENSION NBL(LON)
+* LBL     number of unknowns in each group. DIMENSION LBL(LON)
+*
+*Parameters: output
+* F       solution of the linear system. DIMENSION F(ISEG,L4)
+*
+*-----------------------------------------------------------------------
+*
+      INTEGER ISEG,LON,MU1(*),NBL(LON),LBL(LON)
+      REAL ASS(ISEG,*),F(ISEG,*)
+      REAL, DIMENSION(:), ALLOCATABLE :: T
+*
+      ALLOCATE(T(ISEG))
+      LBL0=0
+      IMAX=0
+      DO 200 ILON=1,LON
+      L4=LBL(ILON)
+      NBANC=NBL(ILON)
+      IF(L4.EQ.1) THEN
+         IMAX=IMAX+1
+CDIR$ SHORTLOOP
+         DO 10 IB=1,NBANC
+         F(IB,LBL0+1)=F(IB,LBL0+1)*ASS(IB,IMAX)
+   10    CONTINUE
+      ELSE IF(LTSW.GT.2) THEN
+         IMAX=MU1(LBL0+L4)
+         K1=MU1(LBL0+1)+1
+         DO 55 I=LBL0+2,LBL0+L4
+         K2=MU1(I)
+         KJ=I-K2+K1
+CDIR$ SHORTLOOP
+         DO 20 IB=1,NBANC
+         T(IB)=-F(IB,I)
+   20    CONTINUE
+         DO 40 K=K1,K2-1
+CDIR$ SHORTLOOP
+         DO 30 IB=1,NBANC
+         T(IB)=T(IB)+F(IB,KJ)*ASS(IB,K)
+   30    CONTINUE
+         KJ=KJ+1
+   40    CONTINUE
+         K1=K2+1
+CDIR$ SHORTLOOP
+         DO 50 IB=1,NBANC
+         F(IB,I)=-T(IB)
+   50    CONTINUE
+   55    CONTINUE
+*
+         DO 65 I=LBL0+1,LBL0+L4
+         K1=MU1(I)
+CDIR$ SHORTLOOP
+         DO 60 IB=1,NBANC
+         F(IB,I)=F(IB,I)*ASS(IB,K1)
+   60    CONTINUE
+   65    CONTINUE
+*
+         K2=IMAX
+         DO 100 I=LBL0+L4,LBL0+2,-1
+CDIR$ SHORTLOOP
+         DO 70 IB=1,NBANC
+         T(IB)=-F(IB,I)
+   70    CONTINUE
+         K1=MU1(I-1)+1
+         KJ=I-K2+K1
+         DO 90 K=K1,K2-1
+CDIR$ SHORTLOOP
+         DO 80 IB=1,NBANC
+         F(IB,KJ)=F(IB,KJ)+ASS(IB,K)*T(IB)
+   80    CONTINUE
+         KJ=KJ+1
+   90    CONTINUE
+         K2=K1-1
+  100    CONTINUE
+      ELSE IF(LTSW.EQ.2) THEN
+         K1=IMAX+2
+         DO 130 I=LBL0+2,LBL0+L4
+         KJ=I-1
+CDIR$ SHORTLOOP
+         DO 110 IB=1,NBANC
+         T(IB)=-F(IB,I)+F(IB,KJ)*ASS(IB,K1)
+  110    CONTINUE
+CDIR$ SHORTLOOP
+         DO 120 IB=1,NBANC
+         F(IB,I)=-T(IB)
+  120    CONTINUE
+         K1=K1+2
+  130    CONTINUE
+*
+         DO 145 I=LBL0+1,LBL0+L4
+         K1=IMAX+2*(I-LBL0)-1
+CDIR$ SHORTLOOP
+         DO 140 IB=1,NBANC
+         F(IB,I)=F(IB,I)*ASS(IB,K1)
+  140    CONTINUE
+  145    CONTINUE
+*
+         K1=IMAX+2*L4-2
+         DO 170 I=LBL0+L4,LBL0+2,-1
+         KJ=I-1
+CDIR$ SHORTLOOP
+         DO 150 IB=1,NBANC
+         T(IB)=-F(IB,I)
+  150    CONTINUE
+CDIR$ SHORTLOOP
+         DO 160 IB=1,NBANC
+         F(IB,KJ)=F(IB,KJ)+ASS(IB,K1)*T(IB)
+  160    CONTINUE
+         K1=K1-2
+  170    CONTINUE
+         IMAX=IMAX+2*L4-1
+      ENDIF
+      LBL0=LBL0+L4
+  200 CONTINUE
+      DEALLOCATE(T)
+      RETURN
+      END
-- 
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