NAG Library Routine Document

S18CDF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     X – REAL (KIND=nag_wp)Input

On entry: the argument $x$ of the function.

Constraint: $\mathbf{X}>0.0$.

2:     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, $\mathbf{X}\le 0.0$: $K_1$ is undefined. On soft failure S18CDF returns zero.

$\mathbf{IFAIL}=2$

On entry, X is too close to zero, as determined by the value of the safe-range parameter X02AMF: there is a danger of causing overflow. On soft failure, S18CDF returns the reciprocal of the safe-range parameter.

7  Accuracy

8  Further Comments

9  Example

9.1  Program Text

Program Text (s18cdfe.f90)

9.2  Program Data

Program Data (s18cdfe.d)

9.3  Program Results

Program Results (s18cdfe.r)