# NAG Library Routine Document

## 1Purpose

e04nuf may be used to supply individual real optional parameters to e04nqf. The initialization routine e04npf must have been called before calling e04nuf.

## 2Specification

Fortran Interface
 Subroutine e04nuf ( cw, 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 Character (8), Intent (Inout) :: cw(*)
#include <nagmk26.h>
 void e04nuf_ (const char *st, const double *rvalue, char cw[], Integer iw[], double rw[], Integer *ifail, const Charlen length_st, const Charlen length_cw)

## 3Description

e04nuf may be used to supply values for real optional parameters to e04nqf. It is only necessary to call e04nuf for those arguments whose values are to be different from their default values. One call to e04nuf 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 e04nuf ('LU Factor Tolerance', factol, cw, iw, rw, ifail)```
Optional parameter settings are preserved following a call to e04nqf 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 e04nqf.
A complete list of optional parameters, their abbreviations, synonyms and default values is given in Section 12 in e04nqf.

None.

## 5Arguments

1:     $\mathbf{string}$ – Character(*)Input
On entry: a single valid keyword of a real optional parameter (as described in Section 12 in e04nqf).
2:     $\mathbf{rvalue}$ – Real (Kind=nag_wp)Input
On entry: the value associated with the keyword in string.
3:     $\mathbf{cw}\left(*\right)$ – Character(8) arrayCommunication Array
Note: the dimension of the array cw must be at least ${\mathbf{lencw}}$ (see e04npf).
4:     $\mathbf{iw}\left(*\right)$ – Integer arrayCommunication Array
Note: the dimension of the array iw must be at least ${\mathbf{leniw}}$ (see e04npf).
5:     $\mathbf{rw}\left(*\right)$ – Real (Kind=nag_wp) arrayCommunication Array
Note: the dimension of the array rw must be at least ${\mathbf{lenrw}}$ (see e04npf).
6:     $\mathbf{ifail}$ – 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 e04npf has not been called.
${\mathbf{ifail}}=2$
The supplied option is invalid. Check that the keywords are neither ambiguous nor misspelt.
${\mathbf{ifail}}=-99$
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.

Not applicable.

## 8Parallelism and Performance

e04nuf is not threaded in any implementation.