NAG Library Function Document
nag_sparse_nherm_fac_sol (f11dqc)
1
Purpose
nag_sparse_nherm_fac_sol (f11dqc) solves a complex sparse non-Hermitian system of linear equations, represented in coordinate storage format, using a restarted generalized minimal residual (RGMRES), conjugate gradient squared (CGS), stabilized bi-conjugate gradient (Bi-CGSTAB), or transpose-free quasi-minimal residual (TFQMR) method, with incomplete preconditioning.
2
Specification
#include <nag.h> |
#include <nagf11.h> |
void |
nag_sparse_nherm_fac_sol (Nag_SparseNsym_Method method,
Integer n,
Integer nnz,
const Complex a[],
Integer la,
const Integer irow[],
const Integer icol[],
const Integer ipivp[],
const Integer ipivq[],
const Integer istr[],
const Integer idiag[],
const Complex b[],
Integer m,
double tol,
Integer maxitn,
Complex x[],
double *rnorm,
Integer *itn,
NagError *fail) |
|
3
Description
nag_sparse_nherm_fac_sol (f11dqc) solves a complex sparse non-Hermitian linear system of equations
using a preconditioned RGMRES (see
Saad and Schultz (1986)), CGS (see
Sonneveld (1989)), Bi-CGSTAB(
) (see
Van der Vorst (1989) and
Sleijpen and Fokkema (1993)), or TFQMR (see
Freund and Nachtigal (1991) and
Freund (1993)) method.
nag_sparse_nherm_fac_sol (f11dqc) uses the incomplete
factorization determined by
nag_sparse_nherm_fac (f11dnc) as the preconditioning matrix. A call to
nag_sparse_nherm_fac_sol (f11dqc) must always be preceded by a call to
nag_sparse_nherm_fac (f11dnc). Alternative preconditioners for the same storage scheme are available by calling
nag_sparse_nherm_sol (f11dsc).
The matrix
, and the preconditioning matrix
, are represented in coordinate storage (CS) format (see
Section 2.1.1 in the f11 Chapter Introduction) in the arrays
a,
irow and
icol, as returned from
nag_sparse_nherm_fac (f11dnc). The array
a holds the nonzero entries in these matrices, while
irow and
icol hold the corresponding row and column indices.
4
References
Freund R W (1993) A transpose-free quasi-minimal residual algorithm for non-Hermitian linear systems SIAM J. Sci. Comput. 14 470–482
Freund R W and Nachtigal N (1991) QMR: a Quasi-Minimal Residual Method for Non-Hermitian Linear Systems Numer. Math. 60 315–339
Saad Y and Schultz M (1986) GMRES: a generalized minimal residual algorithm for solving nonsymmetric linear systems SIAM J. Sci. Statist. Comput. 7 856–869
Sleijpen G L G and Fokkema D R (1993) BiCGSTAB for linear equations involving matrices with complex spectrum ETNA 1 11–32
Sonneveld P (1989) CGS, a fast Lanczos-type solver for nonsymmetric linear systems SIAM J. Sci. Statist. Comput. 10 36–52
Van der Vorst H (1989) Bi-CGSTAB, a fast and smoothly converging variant of Bi-CG for the solution of nonsymmetric linear systems SIAM J. Sci. Statist. Comput. 13 631–644
5
Arguments
- 1:
– Nag_SparseNsym_MethodInput
-
On entry: specifies the iterative method to be used.
- Restarted generalized minimum residual method.
- Conjugate gradient squared method.
- Bi-conjugate gradient stabilized () method.
- Transpose-free quasi-minimal residual method.
Constraint:
, , or .
- 2:
– IntegerInput
-
On entry:
, the order of the matrix
. This
must be the same value as was supplied in the preceding call to
nag_sparse_nherm_fac (f11dnc).
Constraint:
.
- 3:
– IntegerInput
-
On entry: the number of nonzero elements in the matrix
. This
must be the same value as was supplied in the preceding call to
nag_sparse_nherm_fac (f11dnc).
Constraint:
.
- 4:
– const ComplexInput
-
On entry: the values returned in the array
a by a previous call to
nag_sparse_nherm_fac (f11dnc).
- 5:
– IntegerInput
-
On entry: the dimension of the arrays
a,
irow and
icol. This
must be the same value as was supplied in the preceding call to
nag_sparse_nherm_fac (f11dnc).
Constraint:
.
- 6:
– const IntegerInput
- 7:
– const IntegerInput
- 8:
– const IntegerInput
- 9:
– const IntegerInput
- 10:
– const IntegerInput
- 11:
– const IntegerInput
-
On entry: the values returned in arrays
irow,
icol,
ipivp,
ipivq,
istr and
idiag by a previous call to
nag_sparse_nherm_fac (f11dnc).
ipivp and
ipivq are restored on exit.
- 12:
– const ComplexInput
-
On entry: the right-hand side vector .
- 13:
– IntegerInput
-
On entry: if
,
m is the dimension of the restart subspace.
If
,
m is the order
of the polynomial Bi-CGSTAB method.
Otherwise,
m is not referenced.
Constraints:
- if , ;
- if , .
- 14:
– doubleInput
-
On entry: the required tolerance. Let
denote the approximate solution at iteration
, and
the corresponding residual. The algorithm is considered to have converged at iteration
if
If
,
is used, where
is the
machine precision. Otherwise
is used.
Constraint:
.
- 15:
– IntegerInput
-
On entry: the maximum number of iterations allowed.
Constraint:
.
- 16:
– ComplexInput/Output
-
On entry: an initial approximation to the solution vector .
On exit: an improved approximation to the solution vector .
- 17:
– double *Output
-
On exit: the final value of the residual norm
, where
is the output value of
itn.
- 18:
– Integer *Output
-
On exit: the number of iterations carried out.
- 19:
– NagError *Input/Output
-
The NAG error argument (see
Section 3.7 in How to Use the NAG Library and its Documentation).
6
Error Indicators and Warnings
- NE_ACCURACY
-
The required accuracy could not be obtained. However, a reasonable accuracy may have been achieved.
- NE_ALG_FAIL
-
Algorithmic breakdown. A solution is returned, although it is possible that it is completely inaccurate.
- NE_ALLOC_FAIL
-
Dynamic memory allocation failed.
See
Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
- NE_BAD_PARAM
-
On entry, argument had an illegal value.
- NE_CONVERGENCE
-
The solution has not converged after iterations.
- NE_INT
-
On entry, .
Constraint: .
On entry, .
Constraint: .
On entry, .
Constraint: .
- NE_INT_2
-
On entry, and .
Constraint: .
On entry, and .
Constraint: and .
On entry, and .
Constraint: .
- NE_INTERNAL_ERROR
-
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact
NAG for assistance.
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact
NAG for assistance.
See
Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
- NE_INVALID_CS
-
On entry,
,
, and
.
Constraint:
and
.
Check that
a,
irow,
icol,
ipivp,
ipivq,
istr and
idiag have not been corrupted between calls to
nag_sparse_nherm_fac_sol (f11dqc) and
nag_sparse_nherm_fac (f11dnc).
On entry,
,
,
.
Constraint:
and
.
Check that
a,
irow,
icol,
ipivp,
ipivq,
istr and
idiag have not been corrupted between calls to
nag_sparse_nherm_fac_sol (f11dqc) and
nag_sparse_nherm_fac (f11dnc).
- NE_INVALID_CS_PRECOND
-
The CS representation of the preconditioner is invalid.
Check that
a,
irow,
icol,
ipivp,
ipivq,
istr and
idiag have not been corrupted between calls to
nag_sparse_nherm_fac (f11dnc) and
nag_sparse_nherm_fac_sol (f11dqc).
- NE_NO_LICENCE
-
Your licence key may have expired or may not have been installed correctly.
See
Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.
- NE_NOT_STRICTLY_INCREASING
-
On entry,
is out of order:
.
Check that
a,
irow,
icol,
ipivp,
ipivq,
istr and
idiag have not been corrupted between calls to
nag_sparse_nherm_fac_sol (f11dqc) and
nag_sparse_nherm_fac (f11dnc).
On entry, the location (
) is a duplicate:
.
Check that
a,
irow,
icol,
ipivp,
ipivq,
istr and
idiag have not been corrupted between calls to
nag_sparse_nherm_fac_sol (f11dqc) and
nag_sparse_nherm_fac (f11dnc).
- NE_REAL
-
On entry, .
Constraint: .
7
Accuracy
On successful termination, the final residual
, where
, satisfies the termination criterion
The value of the final residual norm is returned in
rnorm.
8
Parallelism and Performance
nag_sparse_nherm_fac_sol (f11dqc) is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.
nag_sparse_nherm_fac_sol (f11dqc) makes calls to BLAS and/or LAPACK routines, which may be threaded within the vendor library used by this implementation. Consult the documentation for the vendor library for further information.
Please consult the
x06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this function. Please also consult the
Users' Note for your implementation for any additional implementation-specific information.
The time taken by
nag_sparse_nherm_fac_sol (f11dqc) for each iteration is roughly proportional to the value of
nnzc returned from the preceding call to
nag_sparse_nherm_fac (f11dnc).
The number of iterations required to achieve a prescribed accuracy cannot be easily determined a priori, as it can depend dramatically on the conditioning and spectrum of the preconditioned coefficient matrix .
10
Example
This example solves a complex sparse non-Hermitian linear system of equations using the CGS method, with incomplete preconditioning.
10.1
Program Text
Program Text (f11dqce.c)
10.2
Program Data
Program Data (f11dqce.d)
10.3
Program Results
Program Results (f11dqce.r)