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45 lines
1.3 KiB
Fortran
45 lines
1.3 KiB
Fortran
*DECK BKSOL
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SUBROUTINE BKSOL (N, A, X)
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C***BEGIN PROLOGUE BKSOL
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C***SUBSIDIARY
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C***PURPOSE Subsidiary to BVSUP
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C***LIBRARY SLATEC
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C***TYPE SINGLE PRECISION (BKSOL-S, DBKSOL-D)
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C***AUTHOR Watts, H. A., (SNLA)
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C***DESCRIPTION
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C
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C **********************************************************************
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C Solution of an upper triangular linear system by
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C back-substitution
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C
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C The matrix A is assumed to be stored in a linear
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C array proceeding in a row-wise manner. The
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C vector X contains the given constant vector on input
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C and contains the solution on return.
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C The actual diagonal of A is unity while a diagonal
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C scaling matrix is stored there.
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C **********************************************************************
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C
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C***SEE ALSO BVSUP
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C***ROUTINES CALLED SDOT
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C***REVISION HISTORY (YYMMDD)
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C 750601 DATE WRITTEN
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900328 Added TYPE section. (WRB)
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C 910722 Updated AUTHOR section. (ALS)
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C***END PROLOGUE BKSOL
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C
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DIMENSION A(*),X(*)
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C
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C***FIRST EXECUTABLE STATEMENT BKSOL
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M=(N*(N+1))/2
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X(N)=X(N)*A(M)
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IF (N .EQ. 1) GO TO 20
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NM1=N-1
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DO 10 K=1,NM1
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J=N-K
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M=M-K-1
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10 X(J)=X(J)*A(M) - SDOT(K,A(M+1),1,X(J+1),1)
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C
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20 RETURN
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END
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