NAG Library Routine Document

C06GBF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     X(N) – REAL (KIND=nag_wp) arrayInput/Output

On entry: if the data values $z_j$ are written as $x_j+i{y}_j$ and if X is declared with bounds $\left(0:\mathbf{N}-1\right)$ in the subroutine from which C06GBF is called, then for $0\le j\le n/2$, $\mathbf{X}\left(j\right)$ must contain $x_j$ ($=x_{n-j}$), while for $n/2<j\le n-1$, $\mathbf{X}\left(j\right)$ must contain ${-y}_j$ ($=y_{n-j}$). In other words, X must contain the Hermitian sequence in Hermitian form. (See also Section 2.1.2 in the C06 Chapter Introduction.)

On exit: the imaginary parts $y_j$ are negated. The real parts $x_j$ are not referenced.

2:     N – INTEGERInput

On entry: $n$, the number of data values.

Constraint: $\mathbf{N}\ge 1$.

3:     IFAIL – INTEGERInput/Output

On entry: IFAIL must be set to $0$, $-1\text{ or }1$. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.

For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{ or }1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is $0$. When the value $-\mathbf{1}\text{ or }\mathbf{1}$ 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).

6  Error Indicators and Warnings

$\mathbf{IFAIL}=1$

On entry,

$\mathbf{N}<1$.

7  Accuracy

8  Further Comments

9  Example

9.1  Program Text

Program Text (c06gbfe.f90)

9.2  Program Data

Program Data (c06gbfe.d)

9.3  Program Results

Program Results (c06gbfe.r)