*DECK ISSOMN
INTEGER FUNCTION ISSOMN (N, B, X, NELT, IA, JA, A, ISYM, MSOLVE,
+ NSAVE, ITOL, TOL, ITMAX, ITER, ERR, IERR, IUNIT, R, Z, P, AP,
+ EMAP, DZ, CSAV, RWORK, IWORK, AK, BNRM, SOLNRM)
C***BEGIN PROLOGUE ISSOMN
C***SUBSIDIARY
C***PURPOSE Preconditioned Orthomin Stop Test.
C This routine calculates the stop test for the Orthomin
C iteration scheme. It returns a non-zero if the error
C estimate (the type of which is determined by ITOL) is
C less than the user specified tolerance TOL.
C***LIBRARY SLATEC (SLAP)
C***CATEGORY D2A4, D2B4
C***TYPE SINGLE PRECISION (ISSOMN-S, ISDOMN-D)
C***KEYWORDS ITERATIVE PRECONDITION, NON-SYMMETRIC LINEAR SYSTEM,
C ORTHOMIN, SLAP, SPARSE, STOP TEST
C***AUTHOR Greenbaum, Anne, (Courant Institute)
C Seager, Mark K., (LLNL)
C Lawrence Livermore National Laboratory
C PO BOX 808, L-60
C Livermore, CA 94550 (510) 423-3141
C seager@llnl.gov
C***DESCRIPTION
C
C *Usage:
C INTEGER N, NELT, IA(NELT), JA(NELT), ISYM, NSAVE, ITOL, ITMAX
C INTEGER ITER, IERR, IUNIT, IWORK(USER DEFINED)
C REAL B(N), X(N), A(NELT), TOL, ERR, R(N), Z(N)
C REAL P(N,0:NSAVE), AP(N,0:NSAVE), EMAP(N,0:NSAVE)
C REAL DZ(N), CSAV(NSAVE), RWORK(USER DEFINED), AK
C REAL BNRM, SOLNRM
C EXTERNAL MSOLVE
C
C IF( ISSOMN(N, B, X, NELT, IA, JA, A, ISYM, MSOLVE, NSAVE,
C $ ITOL, TOL, ITMAX, ITER, ERR, IERR, IUNIT, R, Z, P, AP,
C $ EMAP, DZ, CSAV, RWORK, IWORK, AK, BNRM, SOLNRM)
C $ .NE.0 ) THEN ITERATION CONVERGED
C
C *Arguments:
C N :IN Integer.
C Order of the matrix.
C B :IN Real B(N).
C Right-hand side vector.
C X :IN Real X(N).
C On input X is your initial guess for solution vector.
C On output X is the final approximate solution.
C NELT :IN Integer.
C Number of Non-Zeros stored in A.
C IA :IN Integer IA(NELT).
C JA :IN Integer JA(NELT).
C A :IN Real A(NELT).
C These arrays should hold the matrix A in either the SLAP
C Triad format or the SLAP Column format. See "Description"
C in the SSDOMN or SSLUOM prologue.
C ISYM :IN Integer.
C Flag to indicate symmetric storage format.
C If ISYM=0, all non-zero entries of the matrix are stored.
C If ISYM=1, the matrix is symmetric, and only the upper
C or lower triangle of the matrix is stored.
C MSOLVE :EXT External.
C Name of a routine which solves a linear system MZ = R for
C Z given R with the preconditioning matrix M (M is supplied via
C RWORK and IWORK arrays). The name of the MSOLVE routine must
C be declared external in the calling program. The calling
C sequence to MSOLVE is:
C CALL MSOLVE(N, R, Z, NELT, IA, JA, A, ISYM, RWORK, IWORK)
C Where N is the number of unknowns, R is the right-hand side
C vector and Z is the solution upon return. NELT, IA, JA, A and
C ISYM are defined as above. RWORK is a real array that can
C be used to pass necessary preconditioning information and/or
C workspace to MSOLVE. IWORK is an integer work array for
C the same purpose as RWORK.
C NSAVE :IN Integer.
C Number of direction vectors to save and orthogonalize against.
C ITOL :IN Integer.
C Flag to indicate type of convergence criterion.
C If ITOL=1, iteration stops when the 2-norm of the residual
C divided by the 2-norm of the right-hand side is less than TOL.
C If ITOL=2, iteration stops when the 2-norm of M-inv times the
C residual divided by the 2-norm of M-inv times the right hand
C side is less than TOL, where M-inv is the inverse of the
C diagonal of A.
C ITOL=11 is often useful for checking and comparing different
C routines. For this case, the user must supply the "exact"
C solution or a very accurate approximation (one with an error
C much less than TOL) through a common block,
C COMMON /SSLBLK/ SOLN( )
C If ITOL=11, iteration stops when the 2-norm of the difference
C between the iterative approximation and the user-supplied
C solution divided by the 2-norm of the user-supplied solution
C is less than TOL. Note that this requires the user to set up
C the "COMMON /SSLBLK/ SOLN(LENGTH)" in the calling routine.
C The routine with this declaration should be loaded before the
C stop test so that the correct length is used by the loader.
C This procedure is not standard Fortran and may not work
C correctly on your system (although it has worked on every
C system the authors have tried). If ITOL is not 11 then this
C common block is indeed standard Fortran.
C TOL :IN Real.
C Convergence criterion, as described above.
C ITMAX :IN Integer.
C Maximum number of iterations.
C ITER :IN Integer.
C Current iteration count. (Must be zero on first call.)
C ERR :OUT Real.
C Error estimate of error in final approximate solution, as
C defined by ITOL.
C IERR :OUT Integer.
C Error flag. IERR is set to 3 if ITOL is not one of the
C acceptable values, see above.
C IUNIT :IN Integer.
C Unit number on which to write the error at each iteration,
C if this is desired for monitoring convergence. If unit
C number is 0, no writing will occur.
C R :IN Real R(N).
C The residual R = B-AX.
C Z :WORK Real Z(N).
C P :IN Real P(N,0:NSAVE).
C Workspace used to hold the conjugate direction vector(s).
C AP :IN Real AP(N,0:NSAVE).
C Workspace used to hold the matrix A times the P vector(s).
C EMAP :IN Real EMAP(N,0:NSAVE).
C Workspace used to hold M-inv times the AP vector(s).
C DZ :WORK Real DZ(N).
C Workspace.
C CSAV :DUMMY Real CSAV(NSAVE)
C Reserved for future use.
C RWORK :WORK Real RWORK(USER DEFINED).
C Real array that can be used for workspace in MSOLVE.
C IWORK :WORK Integer IWORK(USER DEFINED).
C Integer array that can be used for workspace in MSOLVE.
C AK :IN Real.
C Current iterate Orthomin iteration parameter.
C BNRM :OUT Real.
C Current solution B-norm, if ITOL = 1 or 2.
C SOLNRM :OUT Real.
C True solution norm, if ITOL = 11.
C
C *Function Return Values:
C 0 : Error estimate (determined by ITOL) is *NOT* less than the
C specified tolerance, TOL. The iteration must continue.
C 1 : Error estimate (determined by ITOL) is less than the
C specified tolerance, TOL. The iteration can be considered
C complete.
C
C *Cautions:
C This routine will attempt to write to the Fortran logical output
C unit IUNIT, if IUNIT .ne. 0. Thus, the user must make sure that
C this logical unit is attached to a file or terminal before calling
C this routine with a non-zero value for IUNIT. This routine does
C not check for the validity of a non-zero IUNIT unit number.
C
C***SEE ALSO SOMN, SSDOMN, SSLUOM
C***ROUTINES CALLED R1MACH, SNRM2
C***COMMON BLOCKS SSLBLK
C***REVISION HISTORY (YYMMDD)
C 871119 DATE WRITTEN
C 881213 Previous REVISION DATE
C 890915 Made changes requested at July 1989 CML Meeting. (MKS)
C 890922 Numerous changes to prologue to make closer to SLATEC
C standard. (FNF)
C 890929 Numerous changes to reduce SP/DP differences. (FNF)
C 891003 Removed C***REFER TO line, per MKS.
C 910411 Prologue converted to Version 4.0 format. (BAB)
C 910502 Removed MSOLVE from ROUTINES CALLED list. (FNF)
C 910506 Made subsidiary to SOMN. (FNF)
C 920407 COMMON BLOCK renamed SSLBLK. (WRB)
C 920511 Added complete declaration section. (WRB)
C 920930 Corrected to not print AK when ITER=0. (FNF)
C 921026 Changed 1.0E10 to R1MACH(2). (FNF)
C 921113 Corrected C***CATEGORY line. (FNF)
C***END PROLOGUE ISSOMN
C .. Scalar Arguments ..
REAL AK, BNRM, ERR, SOLNRM, TOL
INTEGER IERR, ISYM, ITER, ITMAX, ITOL, IUNIT, N, NELT, NSAVE
C .. Array Arguments ..
REAL A(NELT), AP(N,0:NSAVE), B(N), CSAV(NSAVE), DZ(N),
+ EMAP(N,0:NSAVE), P(N,0:NSAVE), R(N), RWORK(*), X(N), Z(N)
INTEGER IA(NELT), IWORK(*), JA(NELT)
C .. Subroutine Arguments ..
EXTERNAL MSOLVE
C .. Arrays in Common ..
REAL SOLN(1)
C .. Local Scalars ..
INTEGER I
C .. External Functions ..
REAL R1MACH, SNRM2
EXTERNAL R1MACH, SNRM2
C .. Common blocks ..
COMMON /SSLBLK/ SOLN
C***FIRST EXECUTABLE STATEMENT ISSOMN
ISSOMN = 0
C
IF( ITOL.EQ.1 ) THEN
C err = ||Residual||/||RightHandSide|| (2-Norms).
IF(ITER .EQ. 0) BNRM = SNRM2(N, B, 1)
ERR = SNRM2(N, R, 1)/BNRM
ELSE IF( ITOL.EQ.2 ) THEN
C -1 -1
C err = ||M Residual||/||M RightHandSide|| (2-Norms).
IF(ITER .EQ. 0) THEN
CALL MSOLVE(N, B, DZ, NELT, IA, JA, A, ISYM, RWORK, IWORK)
BNRM = SNRM2(N, DZ, 1)
ENDIF
ERR = SNRM2(N, Z, 1)/BNRM
ELSE IF( ITOL.EQ.11 ) THEN
C err = ||x-TrueSolution||/||TrueSolution|| (2-Norms).
IF(ITER .EQ. 0) SOLNRM = SNRM2(N, SOLN, 1)
DO 10 I = 1, N
DZ(I) = X(I) - SOLN(I)
10 CONTINUE
ERR = SNRM2(N, DZ, 1)/SOLNRM
ELSE
C
C If we get here ITOL is not one of the acceptable values.
ERR = R1MACH(2)
IERR = 3
ENDIF
C
IF(IUNIT .NE. 0) THEN
IF( ITER.EQ.0 ) THEN
WRITE(IUNIT,1000) NSAVE, N, ITOL
WRITE(IUNIT,1010) ITER, ERR
ELSE
WRITE(IUNIT,1010) ITER, ERR, AK
ENDIF
ENDIF
IF(ERR .LE. TOL) ISSOMN = 1
C
RETURN
1000 FORMAT(' Preconditioned Orthomin(',I3,') for ',
$ 'N, ITOL = ',I5, I5,
$ /' ITER',' Error Estimate',' Alpha')
1010 FORMAT(1X,I4,1X,E16.7,1X,E16.7)
C------------- LAST LINE OF ISSOMN FOLLOWS ----------------------------
END