d02nzf is a setup routine which must be called, if optional inputs need resetting, prior to a continuation call to any of those integrators in Sub-chapter D02M–N that use methods set up by calls to d02mvf, d02nvf or d02nwf.

2 Specification

Fortran Interface

Subroutine d02nzf (

neqmax, tcrit, h, hmin, hmax, maxstp, mxhnil, rwork, ifail)

Integer, Intent (In)	::	neqmax, maxstp, mxhnil
Integer, Intent (Inout)	::	ifail
Real (Kind=nag_wp), Intent (In)	::	tcrit, h, hmin, hmax
Real (Kind=nag_wp), Intent (Inout)	::	rwork(50+4*neqmax)

C Header Interface

#include <nag.h>

void	d02nzf_ (const Integer neqmax, const double tcrit, const double h, const double hmin, const double hmax, const Integer maxstp, const Integer mxhnil, double rwork[], Integer ifail)

The routine may be called by the names d02nzf or nagf_ode_ivp_stiff_contin.

3 Description

d02nzf is provided to permit you to reset many of the arguments which control the integration ‘on the fly’, that is in conjunction with the interrupt facility permitted through the argument itask of the integrator (e.g., see d02nbf). In addition to a number of arguments which you can set initially through one of the integrator setup routines, the step size to be attempted on the next step may be changed.

4 References

See the D02M–N Sub-chapter Introduction.

5 Arguments

1: $neqmax$ – Integer Input: On entry: the value used for the argument neqmax when calling the integrator.

Constraint: $neqmax \geq 1$ .
2: $tcrit$ – Real (Kind=nag_wp) Input: On entry: a point beyond which integration must not be attempted. The use of tcrit is described under the argument itask in the specification for the integrator (e.g., see d02nbf). A value, $0.0$ say, must be specified even if itask subsequently specifies that tcrit will not be used.
3: $h$ – Real (Kind=nag_wp) Input: On entry: the next step size to be attempted. Set $h = 0.0$ if the current value of h is not to be changed.
4: $hmin$ – Real (Kind=nag_wp) Input: On entry: the minimum absolute step size to be allowed. Set $hmin = 0.0$ if this option is not required. Set $hmin < 0.0$ if the current value of hmin is not to be changed.
5: $hmax$ – Real (Kind=nag_wp) Input: On entry: the maximum absolute step size to be allowed. Set $hmax = 0.0$ if this option is not required. Set $hmax < 0.0$ if the current value of hmax is not to be changed.
6: $maxstp$ – Integer Input: On entry: the maximum number of steps to be attempted during one call to the integrator after which it will return with $ifail = 2$ (see d02ncf). Set $maxstp = 0$ if this option is not required. Set $maxstp < 0$ if the current value of maxstp is not to be changed.
7: $mxhnil$ – Integer Input: On entry: the maximum number of warnings printed (if $itrace \geq 0$ , e.g., see d02nbf) per problem when $t + h = t$ on a step ( $h = current step size$ ). If $mxhnil \leq 0$ , a default value of $10$ is assumed.
8: $rwork (50 + 4 \times neqmax)$ – Real (Kind=nag_wp) array Communication Array: This must be the same workspace array as the array rwork supplied to the integrator. It is used to pass information from the integrator to d02nzf and, therefore, its contents must not be changed before calling d02nzf.
9: $ifail$ – Integer Input/Output: On entry: ifail must be set to $0$ , $−1$ or $1$ to set behaviour on detection of an error; these values have no effect when no error is detected.
A value of $0$ causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of $−1$ means that an error message is printed while a value of $1$ means that it is not.

If halting is not appropriate, the value $−1$ or $1$ is recommended. If message printing is undesirable, then the value $1$ is recommended. Otherwise, the value $0$ is recommended. When the value $- 1$ or $1$ is used it is essential to test the value of ifail on exit.

On exit: $ifail = 0$ unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

If on entry

ifail = 0

−1

, explanatory error messages are output on the current error message unit (as defined by x04aaf).

Errors or warnings detected by the routine:

$ifail = 1$: On entry, $neqmax = ⟨ value ⟩$ .
Constraint: $neqmax \geq 1$ .

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.
See Section 7 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.