NAG Library Routine Document

D02PTF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     FEVALS – INTEGEROutput

On exit: the total number of evaluations of $f$ used in the integration so far; this includes evaluations of $f$ required for the secondary integration necessary if D02PQF had previously been called with $\mathbf{METHOD}>0$.

2:     STEPCOST – INTEGEROutput

On exit: the cost in terms of number of evaluations of $f$ of a typical step with the method being used for the integration. The method is specified by the parameter METHOD in a prior call to D02PQF.

3:     WASTE – REAL (KIND=nag_wp)Output

On exit: the number of attempted steps that failed to meet the local error requirement divided by the total number of steps attempted so far in the integration. A ‘large’ fraction indicates that the integrator is having trouble with the problem being solved. This can happen when the problem is ‘stiff’ and also when the solution has discontinuities in a low-order derivative.

4:     STEPSOK – INTEGEROutput

On exit: the number of accepted steps.

5:     HNEXT – REAL (KIND=nag_wp)Output

On exit: the step size the integrator will attempt to use for the next step.

6:     IWSAV($130$) – INTEGER arrayCommunication Array

7:     RWSAV($350$) – REAL (KIND=nag_wp) arrayCommunication Array

Note: the communication RWSAV used by the other routines in the suite must be used here however, only the first $350$ elements will be referenced.

On entry: these must be the same arrays supplied in a previous call to D02PEF or D02PFF. They must remain unchanged between calls.

On exit: information about the integration for use on subsequent calls to D02PEF or D02PFF or other associated routines.

8:     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, a previous call to the setup routine has not been made or the communication arrays have become corrupted, or a catastrophic error has already been detected elsewhere.
You cannot continue integrating the problem.

You cannot call this routine before you have called the integrator.

You have already made one call to this routine after the integrator could not achieve specified accuracy.
You cannot call this routine again.

7  Accuracy

8  Further Comments

9  Example