E04 Chapter Contents
E04 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentE04WHF

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

## 1  Purpose

E04WHF may be used to supply individual real optional parameters to E04WDF. The initialization routine E04WCF must have been called before calling E04WHF.

## 2  Specification

 SUBROUTINE E04WHF ( STRING, RVALUE, IW, RW, IFAIL)
 INTEGER IW(*), IFAIL REAL (KIND=nag_wp) RVALUE, RW(*) CHARACTER(*) STRING

## 3  Description

E04WHF may be used to supply values for real optional parameters to E04WDF. It is only necessary to call E04WHF for those parameters whose values are to be different from their default values. One call to E04WHF sets one parameter 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 11 in E04WDF.

None.

## 5  Parameters

1:     STRING – CHARACTER(*)Input
On entry: a single valid keyword of a real optional parameter (as described in Section 11 in E04WDF).
2:     RVALUE – REAL (KIND=nag_wp)Input
On entry: the value associated with the keyword in STRING.
3:     IW($*$) – INTEGER arrayCommunication Array
Note: the dimension of the array IW must be at least ${\mathbf{LENIW}}$ (see E04WCF).
4:     RW($*$) – REAL (KIND=nag_wp) arrayCommunication Array
Note: the dimension of the array RW must be at least ${\mathbf{LENRW}}$ (see E04WCF).
5:     IFAIL – INTEGERInput/Output
On entry: IFAIL must be set to $0$, $-1\text{​ or ​}1$. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction 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 parameter, 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

If on entry ${\mathbf{IFAIL}}={\mathbf{0}}$ or $-{\mathbf{1}}$, 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.

Not applicable.