* SUBROUTINE JACOBIREVCOM(N, B, X, WORK, LDW, ITER, RESID, \$ INFO, NDX1, NDX2, SCLR1, SCLR2, IJOB) * * -- Iterative template routine -- * Univ. of Tennessee and Oak Ridge National Laboratory * October 1, 1993 * Details of this algorithm are described in "Templates for the * Solution of Linear Systems: Building Blocks for Iterative * Methods", Barrett, Berry, Chan, Demmel, Donato, Dongarra, * Eijkhout, Pozo, Romine, and van der Vorst, SIAM Publications, * 1993. (ftp netlib2.cs.utk.edu; cd linalg; get templates.ps). * * .. Scalar Arguments .. INTEGER N, LDW, ITER, INFO DOUBLE PRECISION RESID INTEGER NDX1, NDX2 DOUBLE PRECISION SCLR1, SCLR2 INTEGER IJOB * .. * .. Array Arguments .. DOUBLE PRECISION B( * ), X( * ), WORK( LDW,* ) * * Purpose * ======= * * JACOBI solves the linear system Ax = b using the Jacobi iterative * method. The matrix splitting should be accomplished before calling * this routine. The diagonal elements of the matrix must be passed into * this routine in the first column of matrix WORK. * * Relative error measured: norm( X - X_1 ) / norm( X ). * * Arguments * ========= * * N (input) INTEGER * On entry, the dimension of the matrix. * Unchanged on exit. * * B (input) DOUBLE PRECISION array, dimension N * On entry, right hand side vector B. * Unchanged on exit. * * X (input/output) DOUBLE PRECISION array, dimension N. * On input, the initial guess. This is commonly set to * the zero vector. * On exit, if INFO = 0, the iterated approximate solution. * * WORK (workspace) DOUBLE PRECISION array, dimension (LDW,3) * Workspace for residual, direction vector, etc. * * LDW (input) INTEGER * The leading dimension of the array WORK. LDW >= max(1,N). * * ITER (input/output) INTEGER * On input, the maximum iterations to be performed. * On output, actual number of iterations performed. * * RESID (input/output) DOUBLE PRECISION * On input, the allowable convergence measure for * norm( x - x_1 ) / norm( x ). * On output, the final value of this measure. * * INFO (output) INTEGER * * = 0: Successful exit. Iterated approximate solution returned. * -5: Erroneous NDX1/NDX2 in INIT call. * -6: Erroneous RLBL. * * > 0: Convergence to tolerance not achieved. This will be * set to the number of iterations performed. * * < 0: Illegal input parameter, or breakdown occurred * during iteration. * * Illegal parameter: * * -1: matrix dimension N < 0 * -2: LDW < N * -3: Maximum number of iterations ITER <= 0. * * NDX1 (input/output) INTEGER. * NDX2 On entry in INIT call contain indices required by interface * level for stopping test. * All other times, used as output, to indicate indices into * WORK[] for the MATVEC, PSOLVE done by the interface level. * * SCLR1 (output) DOUBLE PRECISION. * SCLR2 Used to pass the scalars used in MATVEC. Scalars are reqd because * original routines use dgemv. * * IJOB (input/output) INTEGER. * Used to communicate job code between the two levels. * * BLAS CALLS: DAXPY, DCOPY, DNRM2 * ========================================================== * * .. Parameters .. DOUBLE PRECISION ONE PARAMETER ( ONE = 1.0D+0 ) * .. * .. Local Scalars .. INTEGER I, MAXIT, X1, MM, TEMP, NEED1, NEED2 DOUBLE PRECISION TOL, DNRM2 * * indicates where to resume from. Only valid when IJOB = 2! INTEGER RLBL * * saving all. SAVE * .. * .. External Routines .. * EXTERNAL DAXPY, DCOPY, DNRM2, MATSPLIT * .. * .. Executable Statements .. * * Entry point, so test IJOB IF (IJOB .eq. 1) THEN GOTO 1 ELSEIF (IJOB .eq. 2) THEN * here we do resumption handling IF (RLBL .eq. 2) GOTO 2 IF (RLBL .eq. 3) GOTO 3 * if neither of these, then error INFO = -6 GOTO 20 ENDIF * ***************** 1 CONTINUE ***************** * INFO = 0 MAXIT = ITER TOL = RESID * * Alias workspace columns. * MM = 1 X1 = 2 TEMP = 3 * * Check if caller will need indexing info. * IF( NDX1.NE.-1 ) THEN IF( NDX1.EQ.1 ) THEN NEED1 = ((MM - 1) * LDW) + 1 ELSEIF( NDX1.EQ.2 ) THEN NEED1 = ((X1 - 1) * LDW) + 1 ELSEIF( NDX1.EQ.3 ) THEN NEED1 = ((TEMP - 1) * LDW) + 1 ELSE * report error INFO = -5 GO TO 20 ENDIF ELSE NEED1 = NDX1 ENDIF * IF( NDX2.NE.-1 ) THEN IF( NDX2.EQ.1 ) THEN NEED2 = ((MM - 1) * LDW) + 1 ELSEIF( NDX2.EQ.2 ) THEN NEED2 = ((X1 - 1) * LDW) + 1 ELSEIF( NDX2.EQ.3 ) THEN NEED2 = ((TEMP - 1) * LDW) + 1 ELSE * report error INFO = -5 GO TO 20 ENDIF ELSE NEED2 = NDX2 ENDIF * ITER = 0 * * Form matrix splitting inv(M) and N. * CALL MATSPLIT( ONE, B, WORK( 1,MM ), LDW,'JACOBI','SPLIT' ) * 10 CONTINUE * * Perform Jacobi iteration * ITER = ITER + 1 * * Save the current approximation to X in X1. * CALL DCOPY( N, X, 1, WORK( 1,X1 ), 1 ) * * Apply iteration; result is updated approximation vector x. * CALL DCOPY( N, B, 1, WORK( 1,TEMP ), 1 ) *********CALL MATVEC( ONE, X, ONE, WORK( 1,TEMP ) ) * NDX1 = -1 NDX2 = ((TEMP - 1) * LDW) + 1 * Prepare for return & return SCLR1 = ONE SCLR2 = ONE RLBL = 2 IJOB = 1 RETURN * ***************** 2 CONTINUE ***************** * DO 15 I = 1, N X( I ) = WORK( I,MM ) * WORK( I,TEMP ) 15 CONTINUE * * Compute error and check for acceptable convergence. * CALL DAXPY( N, -ONE, X, 1, WORK( 1,X1 ), 1 ) * *********RESID = DNRM2( N, WORK( 1,X1 ), 1 ) / DNRM2( N, X, 1 ) *********IF ( RESID.LE.TOL ) GO TO 30 * NDX1 = NEED1 NDX2 = NEED2 * Prepare for resumption & return RLBL = 3 IJOB = 2 RETURN * ***************** 3 CONTINUE ***************** IF( INFO.EQ.1 ) GO TO 30 * IF ( ITER.EQ.MAXIT ) THEN INFO = 1 GO TO 20 ENDIF * GO TO 10 * 20 CONTINUE * * Iteration fails. * Reconstruct matrix A. * CALL MATSPLIT( ONE, B, WORK( 1,MM ), LDW, 'JACOBI','RECONSTRUCT' ) * RLBL = -1 IJOB = -1 * RETURN * 30 CONTINUE * * Iteration successful. Reconstruct matrix A. * CALL MATSPLIT( ONE, B, WORK( 1,MM ), LDW, 'JACOBI','RECONSTRUCT' ) * INFO = 0 RLBL = -1 IJOB = -1 * RETURN * * End of JACOBIREVCOM * END