e05zlf is used to query the value of optional parameters available to supported problem solving routines in Chapter E05. Currently the following routines are supported:

2 Specification

Fortran Interface

Subroutine e05zlf (

optstr, ivalue, rvalue, cvalue, optype, iopts, opts, ifail)

Integer, Intent (In)	::	iopts(*)
Integer, Intent (Inout)	::	ifail
Integer, Intent (Out)	::	ivalue, optype
Real (Kind=nag_wp), Intent (In)	::	opts(*)
Real (Kind=nag_wp), Intent (Out)	::	rvalue
Character (*), Intent (In)	::	optstr
Character (*), Intent (Out)	::	cvalue

C Header Interface

#include <nag.h>

void	e05zlf_ (const char optstr, Integer ivalue, double rvalue, char cvalue, Integer optype, const Integer iopts[], const double opts[], Integer ifail, const Charlen length_optstr, const Charlen length_cvalue)

The routine may be called by the names e05zlf or nagf_glopt_optget.

3 Description

e05zlf is used to query the current values of options. It is necessary to initialize optional parameter arrays using e05zkf before any options are queried.

e05zlf will normally return either an integer, real or character value dependent upon the type associated with the optional parameter being queried. Some real and integer options also return additional information in cvalue. Whether the option queried is of integer, real or character type, and whether additional information is returned in cvalue, is indicated by the returned value of optype.

Information on optional parameter names and whether these options are real, integer or character can be found in Section 12 in e05saf, e05sbf, e05ucf and e05usf.

4 References

None.

5 Arguments

1: $optstr$ – Character(*) Input

On entry: a string identifying the option whose current value is required. See Section 12 in e05saf and e05sbf for information on valid options. In addition, the following is a valid option:

$Identify$: e05zlf returns in cvalue the (upper-cased) routine name supplied to e05zkf when the optional parameter arrays iopts and opts were initialized.

2: $ivalue$ – Integer Output

On exit: if the optional parameter supplied in optstr is an integer valued parameter, ivalue will hold its current value.

3: $rvalue$ – Real (Kind=nag_wp) Output

On exit: if the optional parameter supplied in optstr is a real valued parameter, rvalue will hold its current value.

4: $cvalue$ – Character(*) Output

Note: the string returned in cvalue will never exceed

40

characters in length.

On exit: if the optional parameter supplied in optstr is a character valued argument, cvalue will hold its current value. cvalue will also contain additional information for some integer and real valued parameters, as indicated by optype.

5: $optype$ – Integer Output

On exit: indicates whether the optional parameter supplied in optstr is an integer, real or character valued parameter and hence which of ivalue, rvalue or cvalue holds the current value.

$optype = 1$: optstr is an integer valued optional parameter, its current value has been returned in ivalue.
$optype = 2$: optstr is a real valued optional parameter, its current value has been returned in rvalue.
$optype = 3$: optstr is a character valued optional parameter, its current value has been returned in cvalue.
$optype = 4$: optstr is an integer valued optional parameter, its current value has been returned in ivalue. Additional information has been returned in cvalue.
$optype = 5$: optstr is a real valued optional parameter, its current value has been returned in rvalue. Additional information has been returned in cvalue.

6: $iopts (*)$ – Integer array Communication Array

Note: the dimension of this array is dictated by the requirements of associated functions that must have been previously called. This array must be the same array passed as argument iopts in the previous call to e05zkf.

7: $opts (*)$ – Real (Kind=nag_wp) array Communication Array

8: $ifail$ – Integer Input/Output

On entry: ifail must be set to

0

−1

1

to set behaviour on detection of an error; these values have no effect when no error is detected.

A value of

0

causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of

−1

means that an error message is printed while a value of

1

means that it is not.

If halting is not appropriate, the value

−1

1

is recommended. If message printing is undesirable, then the value

1

is recommended. Otherwise, the value

0

is recommended. When the value $- 1$ or $1$ is used it is essential to test the value of ifail on exit.

On exit:

ifail = 0

unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

If on entry

ifail = 0

−1

, explanatory error messages are output on the current error message unit (as defined by x04aaf).

Errors or warnings detected by the routine:

$ifail = 11$: On entry, the $option$ in optstr has not been recognized.

$ifail = 41$: On entry, optstr indicates a character optional parameter, but cvalue is too short to hold the stored value. The returned value will be truncated.

$ifail = 61$: The arrays iopts and opts have either not been initialized, have become corrupted, or are not compatible with this option setting routine.

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.
See Section 7 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 999$: Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.

e05zlf is not threaded in any implementation.

9 Further Comments

Some options have default values which are problem dependent. For example the option Maximum Iterations Completed for e05saf has the default value

1000 \times ndim

. If options such as this are queried before being set, or before the problem solving routine has been called, they will return misleading information in ivalue or rvalue. In some cases, the value of cvalue will be set to DEFAULT to indicate that the real or integer valued optional parameter supplied in optstr is at its default value.