NAG Library Routine Document

f11bff (real_gen_basic_diag)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:     $\mathbf{itn}$ – IntegerOutput

On exit: the number of iterations carried out by f11bef.

2:     $\mathbf{stplhs}$ – Real (Kind=nag_wp)Output

On exit: the current value of the left-hand side of the termination criterion used by f11bef.

3:     $\mathbf{stprhs}$ – Real (Kind=nag_wp)Output

On exit: the current value of the right-hand side of the termination criterion used by f11bef.

4:     $\mathbf{anorm}$ – Real (Kind=nag_wp)Output

On exit: if $\mathbf{iterm}=1$ in the previous call to f11bdf, then anorm contains ${‖A‖}_p$, where $p=1$, $2$ or $\infty$, either supplied or, in the case of $1$ or $\infty$, estimated by f11bef; otherwise $\mathbf{anorm}=0.0$.

5:     $\mathbf{sigmax}$ – Real (Kind=nag_wp)Output

On exit: if $\mathbf{iterm}=2$ in the previous call to f11bdf, the current estimate of the largest singular value ${\sigma }_1\left(\stackrel{-}{A}\right)$ of the preconditioned iteration matrix, either when it has been supplied to f11bdf or it has been estimated by f11bef (see also Sections 3 and 5 in f11bdf); otherwise, $\mathbf{sigmax}=0.0$ is returned.

6:     $\mathbf{work}\left(\mathbf{lwork}\right)$ – Real (Kind=nag_wp) arrayCommunication Array

On entry: the array work as returned by f11bef (see also Sections 3 and 5 in f11bef).

7:     $\mathbf{lwork}$ – IntegerInput

On entry: the dimension of the array work as declared in the (sub)program from which f11bff is called (see also Section 5 in f11bdf).

Constraint: $\mathbf{lwork}\ge 100$.

Note: although the minimum value of lwork ensures the correct functioning of f11bff, a larger value is required by the iterative solver f11bef (see also Section 5 in f11bdf).

8:     $\mathbf{ifail}$ – IntegerInput/Output

On entry: ifail must be set to $0$, $-1\text{ or }1$. If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation for details.

For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{ or }1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this argument, the recommended value is $0$. When the value $-\mathbf{1}\text{ or }\mathbf{1}$ is used it is essential to test the value of ifail on exit.

On exit: $\mathbf{ifail}=\mathbf{0}$ unless the routine detects an error or a warning has been flagged (see Section 6).

6

Error Indicators and Warnings

$\mathbf{ifail}=1$

f11bff has been called out of sequence.

$\mathbf{ifail}=-7$

On entry, $\mathbf{lwork}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{lwork}\ge 100$.

$\mathbf{ifail}=-99$

An unexpected error has been triggered by this routine. Please contact NAG.

See Section 3.9 in How to Use the NAG Library and its Documentation for further information.

$\mathbf{ifail}=-399$

Your licence key may have expired or may not have been installed correctly.

See Section 3.8 in How to Use the NAG Library and its Documentation for further information.

$\mathbf{ifail}=-999$

Dynamic memory allocation failed.

See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example