# NAG Library Routine Document

## 1Purpose

e04whf may be used to supply individual real optional parameters to e04wdf. The initialization routine e04wcf must have been called before calling e04whf.

## 2Specification

Fortran Interface
 Subroutine e04whf ( iw, rw,
 Integer, Intent (Inout) :: iw(*), ifail Real (Kind=nag_wp), Intent (In) :: rvalue Real (Kind=nag_wp), Intent (Inout) :: rw(*) Character (*), Intent (In) :: string
#include <nagmk26.h>
 void e04whf_ (const char *st, const double *rvalue, Integer iw[], double rw[], Integer *ifail, const Charlen length_st)

## 3Description

e04whf may be used to supply values for real optional parameters to e04wdf. It is only necessary to call e04whf for those arguments whose values are to be different from their default values. One call to e04whf sets one argument value.
Each real optional parameter is defined by a single character string in string and the corresponding value in rvalue. For example the following illustrates how the $LU$ stability tolerance could be defined:
factol = 100.0E0
If (illcon) factol = 5.0E0
Call e04whf ('LU Factor Tolerance', factol, iw, rw, ifail)
Optional parameter settings are preserved following a call to e04wdf and so the keyword Defaults is provided to allow you to reset all the optional parameters to their default values before a subsequent call to e04wdf.
A complete list of optional parameters, their abbreviations, synonyms and default values is given in Section 12 in e04wdf.

None.

## 5Arguments

1:     $\mathbf{string}$ – Character(*)Input
On entry: a single valid keyword of a real optional parameter (as described in Section 12 in e04wdf).
2:     $\mathbf{rvalue}$ – Real (Kind=nag_wp)Input
On entry: the value associated with the keyword in string.
3:     $\mathbf{iw}\left(*\right)$ – Integer arrayCommunication Array
Note: the dimension of the array iw must be at least ${\mathbf{leniw}}$ (see e04wcf).
4:     $\mathbf{rw}\left(*\right)$ – Real (Kind=nag_wp) arrayCommunication Array
Note: the dimension of the array rw must be at least ${\mathbf{lenrw}}$ (see e04wcf).
5:     $\mathbf{ifail}$ – IntegerInput/Output
On entry: ifail must be set to $0$, . 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  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  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).

## 6Error Indicators and Warnings

If on entry ${\mathbf{ifail}}=0$ or $-1$, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
${\mathbf{ifail}}=1$
The initialization routine e04wcf has not been called.
${\mathbf{ifail}}=2$
The supplied option is invalid. Check that the keywords are neither ambiguous nor misspelt. The option string is ‘$〈\mathit{\text{value}}〉$’ and ${\mathbf{rvalue}}=〈\mathit{\text{value}}〉$.
${\mathbf{ifail}}=-99$
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.

Not applicable.

## 8Parallelism and Performance

e04whf is not threaded in any implementation.