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87 lines
3.3 KiB
Fortran
87 lines
3.3 KiB
Fortran
*DECK SLVS
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SUBROUTINE SLVS (WM, IWM, X, TEM)
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C***BEGIN PROLOGUE SLVS
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C***SUBSIDIARY
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C***PURPOSE Subsidiary to DEBDF
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C***LIBRARY SLATEC
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C***TYPE SINGLE PRECISION (SLVS-S, DSLVS-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 SLVS solves the linear system in the iteration scheme for the
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C integrator package DEBDF.
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C
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C***SEE ALSO DEBDF
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C***ROUTINES CALLED SGBSL, SGESL
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C***COMMON BLOCKS DEBDF1
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C***REVISION HISTORY (YYMMDD)
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C 800901 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 920422 Changed DIMENSION statement. (WRB)
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C***END PROLOGUE SLVS
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C
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CLLL. OPTIMIZE
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INTEGER IWM, I, IER, IOWND, IOWNS, JSTART, KFLAG, L, MAXORD,
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1 MEBAND, METH, MITER, ML, MU, N, NFE, NJE, NQ, NQU, NST
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REAL WM, X, TEM,
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1 ROWND, ROWNS, EL0, H, HMIN, HMXI, HU, TN, UROUND,
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2 DI, HL0, PHL0, R
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DIMENSION WM(*), IWM(*), X(*), TEM(*)
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COMMON /DEBDF1/ ROWND, ROWNS(210),
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1 EL0, H, HMIN, HMXI, HU, TN, UROUND, IOWND(14), IOWNS(6),
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2 IER, JSTART, KFLAG, L, METH, MITER, MAXORD, N, NQ, NST, NFE,
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3 NJE, NQU
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C-----------------------------------------------------------------------
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C THIS ROUTINE MANAGES THE SOLUTION OF THE LINEAR SYSTEM ARISING FROM
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C A CHORD ITERATION. IT IS CALLED BY STOD IF MITER .NE. 0.
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C IF MITER IS 1 OR 2, IT CALLS SGESL TO ACCOMPLISH THIS.
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C IF MITER = 3 IT UPDATES THE COEFFICIENT H*EL0 IN THE DIAGONAL
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C MATRIX, AND THEN COMPUTES THE SOLUTION.
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C IF MITER IS 4 OR 5, IT CALLS SGBSL.
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C COMMUNICATION WITH SLVS USES THE FOLLOWING VARIABLES..
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C WM = REAL WORK SPACE CONTAINING THE INVERSE DIAGONAL MATRIX IF MITER
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C IS 3 AND THE LU DECOMPOSITION OF THE MATRIX OTHERWISE.
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C STORAGE OF MATRIX ELEMENTS STARTS AT WM(3).
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C WM ALSO CONTAINS THE FOLLOWING MATRIX-RELATED DATA..
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C WM(1) = SQRT(UROUND) (NOT USED HERE),
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C WM(2) = HL0, THE PREVIOUS VALUE OF H*EL0, USED IF MITER = 3.
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C IWM = INTEGER WORK SPACE CONTAINING PIVOT INFORMATION, STARTING AT
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C IWM(21), IF MITER IS 1, 2, 4, OR 5. IWM ALSO CONTAINS THE
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C BAND PARAMETERS ML = IWM(1) AND MU = IWM(2) IF MITER IS 4 OR 5.
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C X = THE RIGHT-HAND SIDE VECTOR ON INPUT, AND THE SOLUTION VECTOR
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C ON OUTPUT, OF LENGTH N.
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C TEM = VECTOR OF WORK SPACE OF LENGTH N, NOT USED IN THIS VERSION.
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C IER = OUTPUT FLAG (IN COMMON). IER = 0 IF NO TROUBLE OCCURRED.
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C IER = -1 IF A SINGULAR MATRIX AROSE WITH MITER = 3.
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C THIS ROUTINE ALSO USES THE COMMON VARIABLES EL0, H, MITER, AND N.
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C-----------------------------------------------------------------------
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C***FIRST EXECUTABLE STATEMENT SLVS
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IER = 0
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GO TO (100, 100, 300, 400, 400), MITER
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100 CALL SGESL (WM(3), N, N, IWM(21), X, 0)
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RETURN
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C
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300 PHL0 = WM(2)
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HL0 = H*EL0
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WM(2) = HL0
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IF (HL0 .EQ. PHL0) GO TO 330
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R = HL0/PHL0
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DO 320 I = 1,N
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DI = 1.0E0 - R*(1.0E0 - 1.0E0/WM(I+2))
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IF (ABS(DI) .EQ. 0.0E0) GO TO 390
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320 WM(I+2) = 1.0E0/DI
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330 DO 340 I = 1,N
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340 X(I) = WM(I+2)*X(I)
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RETURN
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390 IER = -1
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RETURN
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C
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400 ML = IWM(1)
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MU = IWM(2)
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MEBAND = 2*ML + MU + 1
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CALL SGBSL (WM(3), MEBAND, N, ML, MU, IWM(21), X, 0)
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RETURN
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C----------------------- END OF SUBROUTINE SLVS -----------------------
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END
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