NAG AD Library
f07cd_a1w_f (dgttrf_a1w)

Note: _a1w_ denotes that first order adjoints are computed in working precision; this has the corresponding argument type nagad_a1w_w_rtype. Further implementations, for example for higher order differentiation or using the tangent linear approach, may become available at later marks of the NAG AD Library. The method of codifying AD implementations in the routine name and corresponding argument types is described in the NAG AD Library Introduction.

1 Purpose

f07cd_a1w_f is the adjoint version of the primal routine f07cdf (dgttrf).

2 Specification

Fortran Interface
Subroutine f07cd_a1w_f ( ad_handle, n, dl, d, du, du2, ipiv, ifail)
Integer, Intent (In) :: n
Integer, Intent (Inout) :: ifail
Integer, Intent (Out) :: ipiv(n)
Type (nagad_a1w_w_rtype), Intent (Inout) :: dl(*), d(*), du(*)
Type (nagad_a1w_w_rtype), Intent (Out) :: du2(n-2)
Type (c_ptr), Intent (In) :: ad_handle
C++ Header Interface
#include <nagad.h>
void f07cd_a1w_f_ ( void *&ad_handle, const Integer &n, nagad_a1w_w_rtype dl[], nagad_a1w_w_rtype d[], nagad_a1w_w_rtype du[], nagad_a1w_w_rtype du2[], Integer ipiv[], Integer &ifail)
The routine may be called by the names f07cd_a1w_f or nagf_lapacklin_dgttrf_a1w.

3 Description

f07cd_a1w_f is the adjoint version of the primal routine f07cdf (dgttrf).
f07cdf (dgttrf) computes the LU factorization of a real n by n tridiagonal matrix A . For further information see Section 3 in the documentation for f07cdf (dgttrf).

4 References


5 Arguments

In addition to the arguments present in the interface of the primal routine, f07cd_a1w_f includes some arguments specific to AD.
A brief summary of the AD specific arguments is given below. For the remainder, links are provided to the corresponding argument from the primal routine. A tooltip popup for all arguments can be found by hovering over the argument name in Section 2 and in this section.
1: ad_handle – Type (c_ptr) Input
On entry: a handle to the AD configuration data object, as created by x10aa_a1w_f.
2: n – Integer Input
3: dl(*) – Type (nagad_a1w_w_rtype) array Input/Output
4: d(*) – Type (nagad_a1w_w_rtype) array Input/Output
5: du(*) – Type (nagad_a1w_w_rtype) array Input/Output
6: du2(n-2) – Type (nagad_a1w_w_rtype) array Output
7: ipiv(n) – Integer array Output
8: ifail – Integer Input/Output
On entry: must be set to 0, -1  or  1.
On exit: any errors are indicated as described in Section 6.

6 Error Indicators and Warnings

f07cd_a1w_f uses the standard NAG ifail mechanism. Any errors indicated via info values returned by f07cdf may be indicated with the same value returned by ifail. In addition, this routine may return:
An unexpected AD error has been triggered by this routine. Please contact NAG.
See Section 4.5.2 in the NAG AD Library Introduction for further information.
Dynamic memory allocation failed for AD.
See Section 4.5.1 in the NAG AD Library Introduction for further information.

7 Accuracy

Not applicable.

8 Parallelism and Performance

f07cd_a1w_f is not threaded in any implementation.

9 Further Comments


10 Example

The following examples are variants of the example for f07cdf (dgttrf), modified to demonstrate calling the NAG AD Library.
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