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* -*- fortran -*-
SUBROUTINE <_c>CGSREVCOM(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
<rt=real,double precision,real,double precision> RESID
INTEGER NDX1, NDX2
<_t> SCLR1, SCLR2
INTEGER IJOB
* ..
* .. Array Arguments ..
<_t> X( * ), B( * ), WORK( LDW,* )
* ..
*
* Purpose
* =======
*
* CGS solves the linear system Ax = b using the
* Conjugate Gradient Squared iterative method with preconditioning.
*
* Convergence test: ( norm( b - A*x ) / norm( b ) ) .ls. TOL.
* For other measures, see the above reference.
*
* 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. The user should be warned that for
* this particular algorithm, an initial guess close to
* the actual solution can result in divergence.
* On exit, the iterated solution.
*
* WORK (workspace) DOUBLE PRECISION array, dimension (LDW,7)
* Workspace for residual, direction vector, etc.
* Note that vectors PHAT and QHAT, and UHAT and VHAT share
* the same workspace.
*
* LDW (input) INTEGER
* The leading dimension of the array WORK. LDW .gt. = 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( b - A*x ) / norm( b ).
* On ouput, the final value of this measure.
*
* INFO (output) INTEGER
*
* = 0: Successful exit.
* .gt. 0: Convergence not achieved. This will be set
* to the number of iterations performed.
*
* .ls. 0: Illegal input parameter, or breakdown occured
* during iteration.
*
* Illegal parameter:
*
* -1: matrix dimension N .ls. 0
* -2: LDW .ls. N
* -3: Maximum number of iterations ITER .ls. = 0.
* -5: Erroneous NDX1/NDX2 in INIT call.
* -6: Erroneous RLBL.
*
* BREAKDOWN: If RHO become smaller than some tolerance,
* the program will terminate. Here we check
* against tolerance BREAKTOL.
*
* -10: RHO .ls. BREAKTOL: RHO and RTLD have become
* orthogonal.
*
* 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, DDOT, DNRM2, DSCAL
* =============================================================
*
* .. Parameters ..
<rt> ONE, ZERO
PARAMETER ( ONE = 1.0D+0 , ZERO = 0.0D+0 )
* ..
* .. Local Scalars ..
INTEGER R, RTLD, P, PHAT, Q, QHAT, U, UHAT, VHAT,
$ MAXIT, NEED1, NEED2
<rt> TOL, BNRM2, RHOTOL,
$ <sdsd=s,d,s,d>GETBREAK,
$ <rc=ws,d,wsc,dz>NRM2
<_t> ALPHA, BETA, RHO, RHO1, TMPVAL,
$ <xdot=wsdot,ddot,wcdotc,wzdotc>
* ..
* indicates where to resume from. Only valid when IJOB = 2!
INTEGER RLBL
*
* saving all.
SAVE
*
* .. External Funcs ..
EXTERNAL <sdsd>GETBREAK, <_c>AXPY,
$ <_c>COPY, <xdot>, <rc>NRM2, <_c>SCAL
* ..
* .. Intrinsic Funcs ..
INTRINSIC ABS, MAX
* ..
* .. Executable Statements ..
*
* Entry point, 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 (RLBL .eq. 4) GOTO 4
IF (RLBL .eq. 5) GOTO 5
IF (RLBL .eq. 6) GOTO 6
IF (RLBL .eq. 7) GOTO 7
* if neither of these, then error
INFO = -6
GOTO 20
ENDIF
*
*
*****************
1 CONTINUE
*****************
*
INFO = 0
MAXIT = ITER
TOL = RESID
*
* Alias workspace columns.
*
R = 1
RTLD = 2
P = 3
PHAT = 4
Q = 5
QHAT = 6
U = 6
UHAT = 7
VHAT = 7
*
* Check if caller will need indexing info.
*
IF( NDX1.NE.-1 ) THEN
IF( NDX1.EQ.1 ) THEN
NEED1 = ((R - 1) * LDW) + 1
ELSEIF( NDX1.EQ.2 ) THEN
NEED1 = ((RTLD - 1) * LDW) + 1
ELSEIF( NDX1.EQ.3 ) THEN
NEED1 = ((P - 1) * LDW) + 1
ELSEIF( NDX1.EQ.4 ) THEN
NEED1 = ((PHAT - 1) * LDW) + 1
ELSEIF( NDX1.EQ.5 ) THEN
NEED1 = ((Q - 1) * LDW) + 1
ELSEIF( NDX1.EQ.6 ) THEN
NEED1 = ((QHAT - 1) * LDW) + 1
ELSEIF( NDX1.EQ.7 ) THEN
NEED1 = ((U - 1) * LDW) + 1
ELSEIF( NDX1.EQ.8 ) THEN
NEED1 = ((UHAT - 1) * LDW) + 1
ELSEIF( NDX1.EQ.9 ) THEN
NEED1 = ((VHAT - 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 = ((R - 1) * LDW) + 1
ELSEIF( NDX2.EQ.2 ) THEN
NEED2 = ((RTLD - 1) * LDW) + 1
ELSEIF( NDX2.EQ.3 ) THEN
NEED2 = ((P - 1) * LDW) + 1
ELSEIF( NDX2.EQ.4 ) THEN
NEED2 = ((PHAT - 1) * LDW) + 1
ELSEIF( NDX2.EQ.5 ) THEN
NEED2 = ((Q - 1) * LDW) + 1
ELSEIF( NDX2.EQ.6 ) THEN
NEED2 = ((QHAT - 1) * LDW) + 1
ELSEIF( NDX2.EQ.7 ) THEN
NEED2 = ((U - 1) * LDW) + 1
ELSEIF( NDX2.EQ.8 ) THEN
NEED2 = ((UHAT - 1) * LDW) + 1
ELSEIF( NDX2.EQ.9 ) THEN
NEED2 = ((VHAT - 1) * LDW) + 1
ELSE
* report error
INFO = -5
GO TO 20
ENDIF
ELSE
NEED2 = NDX2
ENDIF
*
* Set breakdown tolerance parameter.
*
RHOTOL = <sdsd>GETBREAK()
*
* Set initial residual.
*
CALL <_c>COPY( N, B, 1, WORK(1,R), 1 )
IF ( <rc>NRM2( N, X, 1 ).NE.ZERO ) THEN
*********CALL MATVEC( -ONE, X, ONE, WORK(1,R) )
* Note: using RTLD[] as temp. storage.
*********CALL <_c>COPY(N, X, 1, WORK(1,RTLD), 1)
SCLR1 = -ONE
SCLR2 = ONE
NDX1 = -1
NDX2 = ((R - 1) * LDW) + 1
*
* Prepare for resumption & return
RLBL = 2
IJOB = 3
RETURN
ENDIF
*
*****************
2 CONTINUE
*****************
*
IF ( <rc>NRM2( N, WORK(1,R), 1 ).LE.TOL ) GO TO 30
*
BNRM2 = <rc>NRM2( N, B, 1 )
IF ( BNRM2.EQ.ZERO ) BNRM2 = ONE
*
* Choose RTLD such that initially, (R,RTLD) = RHO is not equal to 0.
* Here we choose RTLD = R.
*
CALL <_c>COPY( N, WORK(1,R), 1, WORK(1,RTLD), 1 )
*
ITER = 0
*
10 CONTINUE
*
* Perform Conjugate Gradient Squared iteration.
*
ITER = ITER + 1
*
RHO = <xdot>( N, WORK(1,RTLD), 1, WORK(1,R), 1 )
IF ( ABS( RHO ).LT.RHOTOL ) GO TO 25
*
* Compute direction vectors U and P.
*
IF ( ITER.GT.1 ) THEN
*
* Compute U.
*
BETA = RHO / RHO1
CALL <_c>COPY( N, WORK(1,R), 1, WORK(1,U), 1 )
CALL <_c>AXPY( N, BETA, WORK(1,Q), 1, WORK(1,U), 1 )
*
* Compute P.
*
CALL <_c>SCAL( N, BETA**2, WORK(1,P), 1 )
CALL <_c>AXPY( N, BETA, WORK(1,Q), 1, WORK(1,P), 1 )
TMPVAL = ONE
CALL <_c>AXPY( N, TMPVAL, WORK(1,U), 1, WORK(1,P), 1 )
ELSE
CALL <_c>COPY( N, WORK(1,R), 1, WORK(1,U), 1 )
CALL <_c>COPY( N, WORK(1,U), 1, WORK(1,P), 1 )
ENDIF
*
* Compute direction adjusting scalar ALPHA.
*
*********CALL PSOLVE( WORK(1,PHAT), WORK(1,P) )
*
NDX1 = ((PHAT - 1) * LDW) + 1
NDX2 = ((P - 1) * LDW) + 1
* Prepare for return & return
RLBL = 3
IJOB = 2
RETURN
*
*****************
3 CONTINUE
*****************
*
*********CALL MATVEC( ONE, WORK(1,PHAT), ZERO, WORK(1,VHAT) )
*
NDX1 = ((PHAT - 1) * LDW) + 1
NDX2 = ((VHAT - 1) * LDW) + 1
* Prepare for return & return
SCLR1 = ONE
SCLR2 = ZERO
RLBL = 4
IJOB = 1
RETURN
*
*****************
4 CONTINUE
*****************
*
ALPHA = RHO / <xdot>( N, WORK(1,RTLD), 1, WORK(1,VHAT), 1 )
*
CALL <_c>COPY( N, WORK(1,U), 1, WORK(1,Q), 1 )
CALL <_c>AXPY( N, -ALPHA, WORK(1,VHAT), 1, WORK(1,Q), 1 )
*
* Compute direction adjusting vectORT UHAT.
* PHAT is being used as temporary storage here.
*
CALL <_c>COPY( N, WORK(1,Q), 1, WORK(1,PHAT), 1 )
TMPVAL = ONE
CALL <_c>AXPY( N, TMPVAL, WORK(1,U), 1, WORK(1,PHAT), 1 )
*********CALL PSOLVE( WORK(1,UHAT), WORK(1,PHAT) )
*
NDX1 = ((UHAT - 1) * LDW) + 1
NDX2 = ((PHAT - 1) * LDW) + 1
* Prepare for return & return
RLBL = 5
IJOB = 2
RETURN
*
*****************
5 CONTINUE
*****************
*
* Compute new solution approximation vector X.
*
CALL <_c>AXPY( N, ALPHA, WORK(1,UHAT), 1, X, 1 )
*
* Compute residual R and check for tolerance.
*
*********CALL MATVEC( ONE, WORK(1,UHAT), ZERO, WORK(1,QHAT) )
*
NDX1 = ((UHAT - 1) * LDW) + 1
NDX2 = ((QHAT - 1) * LDW) + 1
* Prepare for return & return
SCLR1 = ONE
SCLR2 = ZERO
RLBL = 6
IJOB = 1
RETURN
*
*****************
6 CONTINUE
*****************
*
CALL <_c>AXPY( N, -ALPHA, WORK(1,QHAT), 1, WORK(1,R), 1 )
*
*********RESID = <rc>NRM2( N, WORK(1,R), 1 ) / BNRM2
*********IF ( RESID.LE.TOL ) GO TO 30
*
NDX1 = NEED1
NDX2 = NEED2
* Prepare for resumption & return
RLBL = 7
IJOB = 4
RETURN
*
*****************
7 CONTINUE
*****************
IF( INFO.EQ.1 ) GO TO 30
*
IF ( ITER.EQ.MAXIT ) THEN
INFO = 1
GO TO 20
ENDIF
*
RHO1 = RHO
*
GO TO 10
*
20 CONTINUE
*
* Iteration fails.
*
RLBL = -1
IJOB = -1
RETURN
*
25 CONTINUE
*
* Set breakdown flag.
*
IF ( ABS( RHO ).LT.RHOTOL ) INFO = -10
*
30 CONTINUE
*
* Iteration successful; return.
*
INFO = 0
RLBL = -1
IJOB = -1
RETURN
*
* End of CGSREVCOM
*
END
* END SUBROUTINE <_c>CGSREVCOM
|
