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# NAG Toolbox: nag_opt_qpconvex2_sparse_option_string (e04ns)

## Purpose

nag_opt_qpconvex2_sparse_option_string (e04ns) may be used to supply individual optional parameters to nag_opt_qpconvex2_sparse_solve (e04nq). The initialization function nag_opt_qpconvex2_sparse_init (e04np) must have been called before calling nag_opt_qpconvex2_sparse_option_string (e04ns).

## Syntax

[cw, iw, rw, ifail] = e04ns(string, cw, iw, rw)
[cw, iw, rw, ifail] = nag_opt_qpconvex2_sparse_option_string(string, cw, iw, rw)

## Description

nag_opt_qpconvex2_sparse_option_string (e04ns) may be used to supply values for optional parameters to nag_opt_qpconvex2_sparse_solve (e04nq). It is only necessary to call nag_opt_qpconvex2_sparse_option_string (e04ns) for those arguments whose values are to be different from their default values. One call to nag_opt_qpconvex2_sparse_option_string (e04ns) sets one argument value.
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 option must be separated by spaces, or equals signs $\left[=\right]$. Alphabetic characters may be upper or lower case. The string
`Print Level = 1`
is an example of a string used to set an optional parameter. For each option 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 double value. Such numbers may be up to $16$ contiguous characters in Fortran's I, F, E or D formats, terminated by a space if this is not the last item on the line.
For nag_opt_qpconvex2_sparse_option_string (e04ns), each user-specified option is not normally printed as it is defined, but this printing may be turned on using the keyword List. Thus the statement
```[cw, iw, rw, ifail] = e04ns('List', cw, iw, rw);
```
turns on printing of this and subsequent options. Printing may be turned off again using the keyword Nolist.
Optional parameter settings are preserved following a call to nag_opt_qpconvex2_sparse_solve (e04nq) 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 nag_opt_qpconvex2_sparse_solve (e04nq).
A complete list of optional parameters, their abbreviations, synonyms and default values is given in Optional Parameters in nag_opt_qpconvex2_sparse_solve (e04nq).

None.

## Parameters

### Compulsory Input Parameters

1:     $\mathrm{string}$ – string
A single valid option string (see Description in nag_opt_qpconvex2_sparse_option_string (e04ns) and Optional Parameters in nag_opt_qpconvex2_sparse_solve (e04nq)).
2:     $\mathrm{cw}\left(:\right)$ – cell array of strings
The dimension of the array cw must be at least ${\mathbf{lencw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))
3:     $\mathrm{iw}\left(:\right)$int64int32nag_int array
The dimension of the array iw must be at least ${\mathbf{leniw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))
4:     $\mathrm{rw}\left(:\right)$ – double array
The dimension of the array rw must be at least ${\mathbf{lenrw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))

None.

### Output Parameters

1:     $\mathrm{cw}\left(:\right)$ – cell array of strings
The dimension of the array cw will be ${\mathbf{lencw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))
2:     $\mathrm{iw}\left(:\right)$int64int32nag_int array
The dimension of the array iw will be ${\mathbf{leniw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))
3:     $\mathrm{rw}\left(:\right)$ – double array
The dimension of the array rw will be ${\mathbf{lenrw}}$ (see nag_opt_qpconvex2_sparse_init (e04np))
4:     $\mathrm{ifail}$int64int32nag_int scalar
${\mathbf{ifail}}={\mathbf{0}}$ unless the function detects an error (see Error Indicators and Warnings).

## Error Indicators and Warnings

Errors or warnings detected by the function:
${\mathbf{ifail}}=1$
The initialization function nag_opt_qpconvex2_sparse_init (e04np) 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.
${\mathbf{ifail}}=-399$
Your licence key may have expired or may not have been installed correctly.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.

Not applicable.

## Further Comments

nag_opt_qpconvex2_sparse_option_integer_set (e04nt) or nag_opt_qpconvex2_sparse_option_double_set (e04nu) may also be used to supply optional parameters to nag_opt_qpconvex2_sparse_solve (e04nq).

## Example

```function e04ns_example

fprintf('e04ns example results\n\n');

string = 'Iterations limit 50';
% Initialize
[cw, iw, rw, ifail] = e04np;
% Set option
[cw, iw, rw, ifail] = e04ns( ...
'Iterations limit 50', cw, iw, rw);
% Get option value
[ivalue, cw, iw, rw, ifail] = e04nx( ...
'Iterations limit', cw, iw, rw);
fprintf('Iterations limit has been set to %4d\n',ivalue);

```
```e04ns example results

Iterations limit has been set to   50
```

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