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Chapter Introduction
NAG Toolbox

# 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 parameters whose values are to be different from their default values. One call to nag_opt_qpconvex2_sparse_option_string (e04ns) sets one parameter value.
Each optional parameter is defined by a single character string, of up to 72$72$ 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$16$ 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 Section [Optional Parameters] in (e04nq).

None.

## Parameters

### Compulsory Input Parameters

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

None.

None.

### Output Parameters

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

## Error Indicators and Warnings

Errors or warnings detected by the function:
ifail = 1${\mathbf{ifail}}=1$
The initialization function nag_opt_qpconvex2_sparse_init (e04np) has not been called.
ifail = 2${\mathbf{ifail}}=2$
The supplied option is invalid. Check that the keywords are neither ambiguous nor misspelt.

## Accuracy

Not applicable.

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 nag_opt_qpconvex2_sparse_option_string_example
string = 'Iterations limit 50';
[cw, iw, rw, ifail] = nag_opt_qpconvex2_sparse_init();
[cw, iw, rw, ifail] = nag_opt_qpconvex2_sparse_option_string(string, cw, iw, rw);
[ivalue, cw, iw, rw, ifail] = nag_opt_qpconvex2_sparse_option_integer_get(string, cw, iw, rw);
ivalue, ifail
```
```

ivalue =

50

ifail =

0

```
```function e04ns_example
string = 'Iterations limit 50';
[cw, iw, rw, ifail] = e04np;
[cw, iw, rw, ifail] = e04ns(string, cw, iw, rw);
[ivalue, cw, iw, rw, ifail] = e04nx(string, cw, iw, rw);
ivalue, ifail
```
```

ivalue =

50

ifail =

0

```