NAG Library Routine Document

D02LYF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     NEQ – INTEGERInput

On entry: the number of second-order ordinary differential equations solved by D02LAF. It must be the same as the parameter NEQ supplied to D02LAF and D02LXF.

2:     HNEXT – REAL (KIND=nag_wp)Output

On exit: the next step size which D02LAF, if called, would attempt.

3:     HUSED – REAL (KIND=nag_wp)Output

On exit: the last successful step size used by D02LAF.

4:     HSTART – REAL (KIND=nag_wp)Output

On exit: the initial step size used on the current integration problem by D02LAF.

5:     NSUCC – INTEGEROutput

On exit: the number of steps attempted by D02LAF that have been successful since the start of the current problem.

6:     NFAIL – INTEGEROutput

On exit: the number of steps attempted by D02LAF that have failed since the start of the current problem.

7:     NATT – INTEGEROutput

On exit: the number of steps attempted before the initial step was successful. Over a large number of problems the cost of an attempted step of this type is approximately half that of a normal attempted step.

8:     THRES(NEQ) – REAL (KIND=nag_wp) arrayOutput

On exit: the $i$th solution threshold value used in the error control strategy. (See D02LXF.)

9:     THRESP(NEQ) – REAL (KIND=nag_wp) arrayOutput

On exit: the $i$th derivative threshold value used in the error control strategy. (See D02LXF.)

10:   RWORK(LRWORK) – REAL (KIND=nag_wp) arrayCommunication Array

On entry: this must be the same parameter RWORK as supplied to D02LAF. It is used to pass information from D02LAF to D02LYF and therefore the contents of this array must not be changed before calling D02LYF.

11:   LRWORK – INTEGERInput

On entry: the dimension of the array RWORK as declared in the (sub)program from which D02LYF is called.

This must be the same parameter LRWORK as supplied to D02LXF.

12:   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

$\mathbf{IFAIL}=1$

D02LAF has not been called, or one or both of the parameters NEQ and LRWORK does not match the corresponding parameter supplied to D02LXF.

This error exit can be caused if elements of RWORK have been overwritten.

7  Accuracy

8  Further Comments

9  Example