*DECK SLVS SUBROUTINE SLVS (WM, IWM, X, TEM) C***BEGIN PROLOGUE SLVS C***SUBSIDIARY C***PURPOSE Subsidiary to DEBDF C***LIBRARY SLATEC C***TYPE SINGLE PRECISION (SLVS-S, DSLVS-D) C***AUTHOR Watts, H. A., (SNLA) C***DESCRIPTION C C SLVS solves the linear system in the iteration scheme for the C integrator package DEBDF. C C***SEE ALSO DEBDF C***ROUTINES CALLED SGBSL, SGESL C***COMMON BLOCKS DEBDF1 C***REVISION HISTORY (YYMMDD) C 800901 DATE WRITTEN C 891214 Prologue converted to Version 4.0 format. (BAB) C 900328 Added TYPE section. (WRB) C 910722 Updated AUTHOR section. (ALS) C 920422 Changed DIMENSION statement. (WRB) C***END PROLOGUE SLVS C CLLL. OPTIMIZE INTEGER IWM, I, IER, IOWND, IOWNS, JSTART, KFLAG, L, MAXORD, 1 MEBAND, METH, MITER, ML, MU, N, NFE, NJE, NQ, NQU, NST REAL WM, X, TEM, 1 ROWND, ROWNS, EL0, H, HMIN, HMXI, HU, TN, UROUND, 2 DI, HL0, PHL0, R DIMENSION WM(*), IWM(*), X(*), TEM(*) COMMON /DEBDF1/ ROWND, ROWNS(210), 1 EL0, H, HMIN, HMXI, HU, TN, UROUND, IOWND(14), IOWNS(6), 2 IER, JSTART, KFLAG, L, METH, MITER, MAXORD, N, NQ, NST, NFE, 3 NJE, NQU C----------------------------------------------------------------------- C THIS ROUTINE MANAGES THE SOLUTION OF THE LINEAR SYSTEM ARISING FROM C A CHORD ITERATION. IT IS CALLED BY STOD IF MITER .NE. 0. C IF MITER IS 1 OR 2, IT CALLS SGESL TO ACCOMPLISH THIS. C IF MITER = 3 IT UPDATES THE COEFFICIENT H*EL0 IN THE DIAGONAL C MATRIX, AND THEN COMPUTES THE SOLUTION. C IF MITER IS 4 OR 5, IT CALLS SGBSL. C COMMUNICATION WITH SLVS USES THE FOLLOWING VARIABLES.. C WM = REAL WORK SPACE CONTAINING THE INVERSE DIAGONAL MATRIX IF MITER C IS 3 AND THE LU DECOMPOSITION OF THE MATRIX OTHERWISE. C STORAGE OF MATRIX ELEMENTS STARTS AT WM(3). C WM ALSO CONTAINS THE FOLLOWING MATRIX-RELATED DATA.. C WM(1) = SQRT(UROUND) (NOT USED HERE), C WM(2) = HL0, THE PREVIOUS VALUE OF H*EL0, USED IF MITER = 3. C IWM = INTEGER WORK SPACE CONTAINING PIVOT INFORMATION, STARTING AT C IWM(21), IF MITER IS 1, 2, 4, OR 5. IWM ALSO CONTAINS THE C BAND PARAMETERS ML = IWM(1) AND MU = IWM(2) IF MITER IS 4 OR 5. C X = THE RIGHT-HAND SIDE VECTOR ON INPUT, AND THE SOLUTION VECTOR C ON OUTPUT, OF LENGTH N. C TEM = VECTOR OF WORK SPACE OF LENGTH N, NOT USED IN THIS VERSION. C IER = OUTPUT FLAG (IN COMMON). IER = 0 IF NO TROUBLE OCCURRED. C IER = -1 IF A SINGULAR MATRIX AROSE WITH MITER = 3. C THIS ROUTINE ALSO USES THE COMMON VARIABLES EL0, H, MITER, AND N. C----------------------------------------------------------------------- C***FIRST EXECUTABLE STATEMENT SLVS IER = 0 GO TO (100, 100, 300, 400, 400), MITER 100 CALL SGESL (WM(3), N, N, IWM(21), X, 0) RETURN C 300 PHL0 = WM(2) HL0 = H*EL0 WM(2) = HL0 IF (HL0 .EQ. PHL0) GO TO 330 R = HL0/PHL0 DO 320 I = 1,N DI = 1.0E0 - R*(1.0E0 - 1.0E0/WM(I+2)) IF (ABS(DI) .EQ. 0.0E0) GO TO 390 320 WM(I+2) = 1.0E0/DI 330 DO 340 I = 1,N 340 X(I) = WM(I+2)*X(I) RETURN 390 IER = -1 RETURN C 400 ML = IWM(1) MU = IWM(2) MEBAND = 2*ML + MU + 1 CALL SGBSL (WM(3), MEBAND, N, ML, MU, IWM(21), X, 0) RETURN C----------------------- END OF SUBROUTINE SLVS ----------------------- END