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authorstainer_t <thomas.stainer@oecd-nea.org>2025-09-08 13:48:49 +0200
committerstainer_t <thomas.stainer@oecd-nea.org>2025-09-08 13:48:49 +0200
commit7dfcc480ba1e19bd3232349fc733caef94034292 (patch)
tree03ee104eb8846d5cc1a981d267687a729185d3f3 /Utilib/src/ALSBD.f
Initial commit from Polytechnique Montreal
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+*DECK ALSBD
+ SUBROUTINE ALSBD (N,IS,B,IER,MAX)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* solution of a system of linear equations using gaussian elimination
+* with partial pivoting. Double precision version.
+*
+*Copyright:
+* Copyright (C) 1993 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
+* N order of the coefficient matrix.
+* IS number of right hand vectors.
+* B coefficient matrix augmented with the right hand vectors.
+* DIMENSION B(MAX,N+IS)
+* MAX first dimention of matrix B.
+*
+*Parameters: output
+* B solution vectors, starting at B(1,N+1).
+* IER error flag. Execution failure if IER.ne.0.
+*
+*-----------------------------------------------------------------------
+*
+ IMPLICIT DOUBLE PRECISION (A-H,O-Z)
+ DIMENSION B(MAX,*)
+ IN=0
+ M=N+IS
+ IER=0
+ IF (N.EQ.1) GO TO 100
+*
+* SEARCH FOR MAXIMUM PIVOT ON COLUMN JCOL.
+ NM1=N-1
+ NP1=N+1
+ DO 60 JCOL=1,NM1
+ TEST=0.0D0
+ DO 10 I=JCOL,N
+ IF (ABS(B(I,JCOL)).LE.TEST) GO TO 10
+ TEST=ABS(B(I,JCOL))
+ IN=I
+10 CONTINUE
+ IF (TEST.EQ.0.0D0) GO TO 120
+*
+* TRIANGULARIZATION.
+ PMX=B(IN,JCOL)
+ B(IN,JCOL)=B(JCOL,JCOL)
+ IP1=JCOL+1
+ DO 50 J=IP1,M
+ PER=B(IN,J)/PMX
+ B(IN,J)=B(JCOL,J)
+ B(JCOL,J)=PER
+ DO 40 I=IP1,N
+ B(I,J)=B(I,J)-B(I,JCOL)*PER
+40 CONTINUE
+50 CONTINUE
+60 CONTINUE
+ PER=B(N,N)
+ IF (PER.EQ.0.0D0) GO TO 120
+ DO 70 J=NP1,M
+ B(N,J)=B(N,J)/PER
+70 CONTINUE
+*
+* BACK SUBSTITUTION.
+ DO 95 IN=2,N
+ I=N-IN+1
+ IP1=I+1
+ DO 90 J=NP1,M
+ PER=B(I,J)
+ DO 80 K=IP1,N
+ PER=PER-B(I,K)*B(K,J)
+80 CONTINUE
+ B(I,J)=PER
+90 CONTINUE
+95 CONTINUE
+ RETURN
+*
+100 PER=B(1,1)
+ IF (PER.EQ.0.0D0) GO TO 120
+ DO 110 J=2,M
+ B(1,J)=B(1,J)/PER
+110 CONTINUE
+ RETURN
+120 IER=1
+ RETURN
+ END