## 1Purpose

x10bf_a1w_f writes a real value into a callback data object created by x10ba_a1w_f.

## 2Specification

Fortran Interface
 Subroutine x10bf_a1w_f ( x,
 Integer, Intent (Inout) :: ifail Real (Kind=nag_wp), Intent (In) :: x Type (c_ptr), Intent (Inout) :: cb_handle
extern "C" {
 void x10bf_a1w_f_ (void *&cb_handle, const double &x, Integer &ifail)
}
The routine may be called by the names x10bf_a1w_f or nagf_adutils_callback_write_real_a1w.

## 3Description

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. x10bf_a1w_f can be used to insert a real value into the callback data object. In this way real values can be communicated between a procedure argument and its companion callbacks.
Note that data must be written to and read from the callback data object in strict order without omission.

None.

## 5Arguments

1: $\mathbf{cb_handle}$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.
2: $\mathbf{x}$Real (Kind=nag_wp) Input
On entry: a real value, $x$, to be inserted into the callback data object.
3: $\mathbf{ifail}$Integer Input/Output
On entry: ifail must be set to $0$, . 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 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 is used it is essential to test the value of ifail on exit.
On exit: ${\mathbf{ifail}}={\mathbf{0}}$ unless the routine detects an error or a warning has been flagged (see Section 6).

## 6Error Indicators and Warnings

If on entry ${\mathbf{ifail}}=0$ or $-1$, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
${\mathbf{ifail}}=1$
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.
${\mathbf{ifail}}=-99$
See Section 7 in the Introduction to the NAG Library FL Interface for further information.
${\mathbf{ifail}}=-399$
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.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.

Not applicable.

## 8Parallelism and Performance

x10bf_a1w_f is not threaded in any implementation.