E05 Chapter Contents
E05 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentE05JCF

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

E05JCF may be used to supply optional parameters to E05JBF from an external file. The initialization routine E05JAF must have been called before calling E05JCF.

## 2  Specification

 SUBROUTINE E05JCF ( IOPTS, COMM, LCOMM, IFAIL)
 INTEGER IOPTS, LCOMM, IFAIL REAL (KIND=nag_wp) COMM(LCOMM)

## 3  Description

E05JCF may be used to supply values for optional parameters to E05JBF. E05JCF reads an external file and each line of the file defines a single optional parameter. It is only necessary to supply values for those parameters whose values are to be different from their default values.
Each optional parameter is defined by a single character string, of up to $72$ characters, consisting of one or more items. The items associated with a given optional parameter must be separated by spaces, or equals signs $\left[=\right]$. Alphabetic characters may be upper or lower case. The string
`Static Limit = 100`
is an example of a string used to set an optional parameter. For each optional parameter the string contains one or more of the following items:
 – a mandatory keyword; – a phrase that qualifies the keyword; – a number that specifies an integer or real value. Such numbers may be up to $16$ contiguous characters.
Blank strings and comments are ignored. A comment begins with an asterisk (*) and all subsequent characters in the string are regarded as part of the comment.
The implied data type (character, integer or real) of each value to set must match that expected by the corresponding optional parameter.
The file containing the optional parameters must start with Begin and must finish with End. An example of a valid options file is:
```Begin * Example options file
Static Limit = 500
End
```
Optional parameter settings are preserved following a call to E05JBF 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 E05JBF.
A complete list of optional parameters, their symbolic names and default values is given in Section 11 in E05JBF.

None.

## 5  Parameters

1:     IOPTS – INTEGERInput
On entry: the unit number of the option file to be read.
Constraint: IOPTS is a valid unit open for reading.
2:     COMM(LCOMM) – REAL (KIND=nag_wp) arrayCommunication Array
On exit: COMM must not be altered between calls to any of the routines E05JBF, E05JCF, E05JDF, E05JEF, E05JFF, E05JGF, E05JHF, E05JJF, E05JKF and E05JLF.
3:     LCOMM – INTEGERInput
On entry: the dimension of the array COMM as declared in the (sub)program from which E05JCF is called.
Constraint: ${\mathbf{LCOMM}}\ge 100$.
4:     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:
${\mathbf{IFAIL}}=1$
 On entry, ${\mathbf{LCOMM}}<100$, or the initialization routine E05JAF has not been called.
${\mathbf{IFAIL}}=2$
Could not read options file on unit IOPTS. This may be because:
 (a) IOPTS is not a valid unit number; (b) a file is not associated with unit IOPTS, or if it is, is unavailable for read access; (c) one or more lines of the options file are invalid. A keyword or keyword combination was not recognized; (d) Begin was found, but end-of-file was found before End was found; (e) end-of-file was found before Begin was found.
In cases (c) and (d) all optional parameters that were set from the file before the error was encountered will remain set on exit.
${\mathbf{IFAIL}}=3$
An option value to be set was out of range with respect to the corresponding optional parameter given. See Section 11 in E05JBF for allowable values of the optional parameters.
${\mathbf{IFAIL}}=5$
A supplied string associated with a numeric value could not be parsed. Check that all such strings specify valid integer or real values.

## 7  Accuracy

Not applicable.

E05JDF, E05JEF, E05JFF or E05JGF may also be used to supply optional parameters to E05JBF.

## 9  Example

This example finds the global minimum of the ‘peaks’ function in two dimensions
 $Fx,y = 3 1-x 2 exp - x 2 - y+1 2 -10 x 5 - x 3 - y 5 exp - x 2 - y 2 - 1 3 exp - x+1 2 - y 2$
on the box $\left[-3,3\right]×\left[-3,3\right]$.
The function $F$ has several local minima and one global minimum in the given box. The global minimum is approximately located at $\left(0.23,-1.63\right)$, where the function value is approximately $-6.55$.
By specifying an initialization list via LIST, NUMPTS and INITPT we can start E05JBF looking close to one of the local minima and check that it really does move away from that point to one of the global minima.
More precisely, we choose $\left(-1,0\right)$ as our initial point (see Section 9.3), and let the initialization list be
 $-3 -1 3 -3 0 3 .$
This example solves the optimization problem using some of the optional parameters described in Section 11 in E05JBF.

### 9.1  Program Text

Program Text (e05jcfe.f90)

### 9.2  Program Data

Program Data (e05jcfe.d)

Program Options (e05jcfe.opt)

### 9.3  Program Results

Program Results (e05jcfe.r)