f11bfc is the third in a suite of three functions for the iterative solution of a real general (nonsymmetric) system of simultaneous linear equations (see Golub and Van Loan (1996)). f11bfc returns information about the computations during an iteration and/or after this has been completed. The first function of the suite, f11bdc, is a setup function; the second function, f11bec, is the iterative solver itself.

These three functions are suitable for the solution of large sparse general (nonsymmetric) systems of equations.

2 Specification

#include <nag.h>

void	f11bfc (Integer itn, double stplhs, double stprhs, double anorm, double sigmax, const double work[], Integer lwork, NagError fail)

The function may be called by the names: f11bfc, nag_sparse_real_gen_basic_diag or nag_sparse_nsym_basic_diagnostic.

3 Description

f11bfc returns information about the solution process. It can be called either during a monitoring step of f11bec or after f11bec has completed its tasks. Calling f11bfc at any other time will result in an error condition being raised.

For further information you should read the documentation for f11bdc and f11bec.

4 References

Golub G H and Van Loan C F (1996) Matrix Computations (3rd Edition) Johns Hopkins University Press, Baltimore

5 Arguments

1: $itn$ – Integer * Output: On exit: the number of iterations carried out by f11bec.
2: $stplhs$ – double * Output: On exit: the current value of the left-hand side of the termination criterion used by f11bec.
3: $stprhs$ – double * Output: On exit: the current value of the right-hand side of the termination criterion used by f11bec.
4: $anorm$ – double * Output: On exit: if $iterm = 1$ in the previous call to f11bdc, then anorm contains ${‖ A ‖}_{p}$ , where $p = 1$ , $2$ or $\infty$ , either supplied or, in the case of $1$ or $\infty$ , estimated by f11bec; otherwise $anorm = 0.0$ .
5: $sigmax$ – double * Output: On exit: if $iterm = 2$ in the previous call to f11bdc, the current estimate of the largest singular value $σ_{1} (\bar{A})$ of the preconditioned iteration matrix, either when it has been supplied to f11bdc or it has been estimated by f11bec (see also Sections 3 and 5 in f11bdc); otherwise, $sigmax = 0.0$ is returned.
6: $work [lwork]$ – const double Communication Array: On entry: the array work as returned by f11bec (see also Sections 3 and 5 in f11bec).
7: $lwork$ – Integer Input: On entry: the dimension of the array work (see also Section 5 in f11bdc).

Constraint: $lwork \geq 100$ .

Note: although the minimum value of lwork ensures the correct functioning of f11bfc, a larger value is required by the iterative solver f11bec (see also Section 5 in f11bdc).
8: $fail$ – NagError * Input/Output: The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6 Error Indicators and Warnings

NE_ALLOC_FAIL: Dynamic memory allocation failed.
See Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.
NE_BAD_PARAM: On entry, argument $⟨ value ⟩$ had an illegal value.
NE_INT: On entry, $lwork = ⟨ value ⟩$ .
Constraint: $lwork \geq 100$ .
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.
See Section 7.5 in the Introduction to the NAG Library CL Interface for further information.
NE_NO_LICENCE: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library CL Interface for further information.
NE_OUT_OF_SEQUENCE: f11bfc has been called out of sequence.