# NAG Library Routine Document

## 1Purpose

x10aa_a1w_f initializes a configuration data structure for the NAG AD Library. It must be called prior to the first call to any routine from the NAG AD Library as listed in the NAG AD Library Introduction including any other routine in Chapter X10.

## 2Specification

Fortran Interface
 Subroutine x10aa_a1w_f (
 Integer, Intent (Inout) :: ifail Type (c_ptr), Intent (Out) :: ad_handle
extern "C" {
 void x10aa_a1w_f_ (void *&ad_handle, Integer &ifail)
}
 Declare PtrSafe Sub X10AAF Lib "libname" ( _ ad_handle As LongPtr, ifail As Long)

## 3Description

x10aa_a1w_f creates and initializes a configuration data object and returns a handle to the data object. This handle may then be passed to any routine in the NAG AD Library as listed in the NAG AD Library Introduction. The object must always be destroyed by a call to x10ab_a1w_f prior to exiting the application in which it was created.
The returned handle can also be passed to x10ac_a1w_f and x10ad_a1w_f to repectively set and get the algorithmic mode (see the X10 Chapter Introduction).

### 3.1Life Cycle of the Handle

Each handle should pass four stages in its life: initialization; mode setting; problem solution using the NAG AD Library; and, destruction.
The initialization by x10aa_a1w_f and destruction by x10ab_a1w_f mark the beginning and the end of the life of the handle. During this time the handle must only be modified by NAG AD Library routines. Working with a handle which has not been properly initialized is potentially very dangerous as it may cause unpredictable behaviour.
After the handle has been initialized, two routines are provided to set or get the computational mode to be used in algorithmic differentiation.
The handle is then passed to the computational routines of the NAG AD Library.
Note that separate configuration data objects can be initialized to contain different computational modes; for example, one handle for the symbolic computational mode (to be used when symbolic adjoints are possible and required) and one handle to contain the algorithmic computational mode.
When all AD computation is completed, the handle must be destroyed by x10ab_a1w_f.

None.

## 5Arguments

1:     $\mathbf{ad_handle}$ – Type (c_ptr)Output
Note: ad_handle does not need to be set on input.
On exit: holds a handle to the internal data structure where the computational AD configuration data, e.g., mode, is defined. You must not change the handle other than via NAG AD Library calls until it is destroyed by x10ab_a1w_f.
2:     $\mathbf{ifail}$ – IntegerInput/Output
On entry: ifail must be set to $0$, . If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation 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:
${\mathbf{ifail}}=-99$
See Section 3.9 in How to Use the NAG Library and its Documentation for further information.
${\mathbf{ifail}}=-399$
Your licence key may have expired or may not have been installed correctly.
See Section 3.8 in How to Use the NAG Library and its Documentation for further information.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.
See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

Not applicable.

## 8Parallelism and Performance

x10aa_a1w_f is not threaded in any implementation.