# NAG C Library Function Document

## 1Purpose

nag_opt_sparse_convex_qp_option_set_double (e04nuc) may be used to supply individual double optional parameters to nag_opt_sparse_convex_qp_solve (e04nqc). The initialization function nag_opt_sparse_convex_qp_init (e04npc) must have been called before calling nag_opt_sparse_convex_qp_option_set_double (e04nuc).

## 2Specification

 #include #include
 void nag_opt_sparse_convex_qp_option_set_double (const char *string, double rvalue, Nag_E04State *state, NagError *fail)

## 3Description

nag_opt_sparse_convex_qp_option_set_double (e04nuc) may be used to supply values for double optional parameters to nag_opt_sparse_convex_qp_solve (e04nqc). It is only necessary to call nag_opt_sparse_convex_qp_option_set_double (e04nuc) for those arguments whose values are to be different from their default values. One call to nag_opt_sparse_convex_qp_option_set_double (e04nuc) sets one argument value.
Each double 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 = 100.0;
if (illcon) factol = 5.0;
e04nuc ("LU Factor Tolerance", factol, &state, &fail);```
Optional parameter settings are preserved following a call to nag_opt_sparse_convex_qp_solve (e04nqc) and so the keyword ${\mathbf{Defaults}}$ is provided to allow you to reset all the optional parameters to their default values before a subsequent call to nag_opt_sparse_convex_qp_solve (e04nqc).
A complete list of optional parameters, their abbreviations, synonyms and default values is given in Section 12 in nag_opt_sparse_convex_qp_solve (e04nqc).

None.

## 5Arguments

1:    $\mathbf{string}$const char *Input
On entry: a single valid keyword of a double optional parameter (as described in Section 12 in nag_opt_sparse_convex_qp_solve (e04nqc)).
2:    $\mathbf{rvalue}$doubleInput
On entry: the value associated with the keyword in string.
3:    $\mathbf{state}$Nag_E04State *Communication Structure
state contains internal information required for functions in this suite. It must not be modified in any way.
4:    $\mathbf{fail}$NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

## 6Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.
NE_E04_OPTION_INVALID
The supplied option is invalid. Check that the keywords are neither ambiguous nor misspelt. The option string is ‘$〈\mathit{\text{value}}〉$’ and ${\mathbf{rvalue}}=〈\mathit{\text{value}}〉$.
NE_E04NPC_NOT_INIT
The initialization function nag_opt_sparse_convex_qp_init (e04npc) has not been called.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

Not applicable.

## 8Parallelism and Performance

nag_opt_sparse_convex_qp_option_set_double (e04nuc) is not threaded in any implementation.