Settings help

## 1Purpose

x10bd_AD_f gets the callback computational mode from a configuration data structure for the NAG AD Library as created by a prior call to x10aa_AD_f.

## 2Specification

Fortran Interface
 Integer, Intent (Inout) :: ifail Integer, Intent (Out) :: mode Type (c_ptr), Intent (In) :: ad_handle
To be consistent with the naming scheme for other routines in the AD Library, two routines are available with names formed by replacing AD in the above by a1w or a1t1w.
namespace nag {
 void x10bd (void *&ad_handle, Integer &mode, Integer &ifail)
}
}
This function is applicable when symbolic adjoints are being used.

## 3Description

Note that in the case where the algorithmic computation mode is being used and the primal callback operation involves only standard operations and intrinsic functions then the callback computational mode is not relevant and no companion callback need be supplied. When the symbolic_expert computational mode is being used the callback computational mode must be interrogated to determine the form of operation required, even when this is to be performed using operator overloading rather than via companion callbacks. I dco/c++ is not being used, this also applies to symbolic computational mode. See Section 10 in c05ay_a1w_f.

### 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_AD_f and destruction by x10ab_AD_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 callback computational mode to determine the form of computation to be performed by a supplied procedure argument. If, for example, a callback needs to know the computational mode in order to provide differentials appropriately, x10bd_AD_f will return the current computational mode as stored in the ad_handle.
When all AD computation is completed, the handle must be destroyed by x10ab_AD_f.

None.

## 5Arguments

1: $\mathbf{ad_handle}$Pointer to AD Data Input
On entry: a handle to the AD configuration data object, as created by x10aa_AD_f.
2: $\mathbf{mode}$Integer Output
On exit: the callback computational mode as stored in the AD configuration data object with handle ad_handle.
${\mathbf{mode}}=\mathit{nagad_primal}$
The current callback is expected to perform the primal calculation.
${\mathbf{mode}}=\mathit{nagad_dstate}$
The current callback is expected to return the derivatives of the primal calculation with respect to real-valued input arguments.
${\mathbf{mode}}=\mathit{nagad_dparam}$
The current callback is expected to return the derivatives of the primal calculation with respect to user-supplied real-valued inputs (e.g., in ruser).
${\mathbf{mode}}=\mathit{nagad_dall}$
The current callback is expected to return derivatives of the primal calculation with respect to both active input arguments and active supplied parameters (i.e., combining nagad_dstate and nagad_dparam).
3: $\mathbf{ifail}$Integer Input/Output
On entry: ifail must be set to $0$, $-1$ or $1$ 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 $-1$ or $1$ is recommended. If message printing is undesirable, then the value $1$ is recommended. Otherwise, the value $0$ is recommended. When the value $-\mathbf{1}$ or $\mathbf{1}$ 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: ad_handle is not a valid handle for the AD computational data object. Either ad_handle has not been initialized or it has become corrupted.
${\mathbf{ifail}}=2$
Unexpected value of mode set on exit, ${\mathbf{mode}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{mode}}=\mathit{nagad_primal}$, $\mathit{nagad_dstate}$, $\mathit{nagad_dparam}$ or $\mathit{nagad_dall}$.
${\mathbf{ifail}}=-99$
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.