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88 lines
3.4 KiB
Fortran
88 lines
3.4 KiB
Fortran
*DECK DSDI
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SUBROUTINE DSDI (N, B, X, NELT, IA, JA, A, ISYM, RWORK, IWORK)
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C***BEGIN PROLOGUE DSDI
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C***PURPOSE Diagonal Matrix Vector Multiply.
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C Routine to calculate the product X = DIAG*B, where DIAG
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C is a diagonal matrix.
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C***LIBRARY SLATEC (SLAP)
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C***CATEGORY D1B4
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C***TYPE DOUBLE PRECISION (SSDI-S, DSDI-D)
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C***KEYWORDS ITERATIVE PRECONDITION, LINEAR SYSTEM SOLVE, SLAP, SPARSE
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C***AUTHOR Greenbaum, Anne, (Courant Institute)
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C Seager, Mark K., (LLNL)
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C Lawrence Livermore National Laboratory
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C PO BOX 808, L-60
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C Livermore, CA 94550 (510) 423-3141
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C seager@llnl.gov
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C***DESCRIPTION
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C
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C *Usage:
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C INTEGER N, NELT, IA(NELT), JA(NELT), ISYM, IWORK(10)
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C DOUBLE PRECISION B(N), X(N), A(NELT), RWORK(USER DEFINED)
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C
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C CALL DSDI (N, B, X, NELT, IA, JA, A, ISYM, RWORK, IWORK)
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C
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C *Arguments:
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C N :IN Integer
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C Order of the Matrix.
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C B :IN Double Precision B(N).
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C Vector to multiply the diagonal by.
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C X :OUT Double Precision X(N).
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C Result of DIAG*B.
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C NELT :DUMMY Integer.
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C IA :DUMMY Integer IA(NELT).
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C JA :DUMMY Integer JA(NELT).
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C A :DUMMY Double Precision A(NELT).
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C ISYM :DUMMY Integer.
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C These are for compatibility with SLAP MSOLVE calling sequence.
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C RWORK :IN Double Precision RWORK(USER DEFINED).
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C Work array holding the diagonal of some matrix to scale
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C B by. This array must be set by the user or by a call
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C to the SLAP routine DSDS or DSD2S. The length of RWORK
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C must be >= IWORK(4)+N.
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C IWORK :IN Integer IWORK(10).
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C IWORK(4) holds the offset into RWORK for the diagonal matrix
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C to scale B by. This is usually set up by the SLAP pre-
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C conditioner setup routines DSDS or DSD2S.
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C
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C *Description:
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C This routine is supplied with the SLAP package to perform
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C the MSOLVE operation for iterative drivers that require
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C diagonal Scaling (e.g., DSDCG, DSDBCG). It conforms
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C to the SLAP MSOLVE CALLING CONVENTION and hence does not
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C require an interface routine as do some of the other pre-
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C conditioners supplied with SLAP.
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C
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C***SEE ALSO DSDS, DSD2S
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C***REFERENCES (NONE)
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 871119 DATE WRITTEN
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C 881213 Previous REVISION DATE
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C 890915 Made changes requested at July 1989 CML Meeting. (MKS)
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C 890922 Numerous changes to prologue to make closer to SLATEC
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C standard. (FNF)
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C 890929 Numerous changes to reduce SP/DP differences. (FNF)
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C 910411 Prologue converted to Version 4.0 format. (BAB)
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C 920511 Added complete declaration section. (WRB)
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C 930701 Updated CATEGORY section. (FNF, WRB)
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C***END PROLOGUE DSDI
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C .. Scalar Arguments ..
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INTEGER ISYM, N, NELT
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C .. Array Arguments ..
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DOUBLE PRECISION A(NELT), B(N), RWORK(*), X(N)
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INTEGER IA(NELT), IWORK(10), JA(NELT)
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C .. Local Scalars ..
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INTEGER I, LOCD
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C***FIRST EXECUTABLE STATEMENT DSDI
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C
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C Determine where the inverse of the diagonal
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C is in the work array and then scale by it.
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C
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LOCD = IWORK(4) - 1
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DO 10 I = 1, N
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X(I) = RWORK(LOCD+I)*B(I)
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10 CONTINUE
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RETURN
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C------------- LAST LINE OF DSDI FOLLOWS ----------------------------
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END
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