For routines where it is necessary to perform callback operations via one or more companion callbacks, data must be passed between the procedure argument and any such companion callback via a callback data object as created by x10ba_a1w_f. x10cf_a1w_f can be used to extract a real value from the callback data object. In this way real values can be communicated between a procedure argument and its companion callbacks.

Note that writing to and reading from a callback data object must be performed in strict order without omission. Reading a data item from the object is equivalent to removing that item from a data stack; reading is therefore not passive, but updates the callback data object.

4 References

None.

5 Arguments

1: $cb_handle$ – Type (c_ptr) Input/Output: On entry: will contain a handle to the callback data object.

On exit: will contain a handle to the updated callback data object, with data item removed from data stack.
2: $x$ – Real (Kind=nag_wp) Output: On exit: a real value, $x$ , to be extracted from the callback data object.
3: $ifail$ – Integer Input/Output: On entry: ifail must be set to $0$ , $- 1 or 1$ . If you are unfamiliar with this argument you should refer to Section 4 in the Introduction to the NAG Library FL Interface for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value $- 1 or 1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this argument, the recommended value is $0$ . 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:

$ifail = 1$: On entry, cb_handle does not define a valid handle to a NAG AD callback data object. It has not been initialized or has been corrupted.

$ifail = - 99$: 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

x10cf_a1w_f is not threaded in any implementation.

9 Further Comments

None.

10 Example

See examples for computational routines in the NAG AD Library, for example, Section 10 in c05ay_a1w_f.

NAG Library Manual, Mark 27

Interfaces: FL CL AD

NAG AD Interface Introduction

X10 (Adutils) Chapter Contents

X10 (Adutils) Chapter Introduction

x10cf: FL CL AD

NAG AD Libraryx10cf_a1w_f (callback_​read_​real_a1w)

▸▿ Contents

1 Purpose

2 Specification

3 Description