# NAG FL Interfaced02nzf (ivp_​stiff_​contin)

## ▸▿ Contents

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## 1Purpose

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.

## 2Specification

Fortran Interface
 Subroutine d02nzf ( h, hmin, hmax,
 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)
#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.

## 3Description

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.

## 4References

See the D02M–N Sub-chapter Introduction.

## 5Arguments

1: $\mathbf{neqmax}$Integer Input
On entry: the value used for the argument neqmax when calling the integrator.
Constraint: ${\mathbf{neqmax}}\ge 1$.
2: $\mathbf{tcrit}$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: $\mathbf{h}$Real (Kind=nag_wp) Input
On entry: the next step size to be attempted. Set ${\mathbf{h}}=0.0$ if the current value of h is not to be changed.
4: $\mathbf{hmin}$Real (Kind=nag_wp) Input
On entry: the minimum absolute step size to be allowed. Set ${\mathbf{hmin}}=0.0$ if this option is not required. Set ${\mathbf{hmin}}<0.0$ if the current value of hmin is not to be changed.
5: $\mathbf{hmax}$Real (Kind=nag_wp) Input
On entry: the maximum absolute step size to be allowed. Set ${\mathbf{hmax}}=0.0$ if this option is not required. Set ${\mathbf{hmax}}<0.0$ if the current value of hmax is not to be changed.
6: $\mathbf{maxstp}$Integer Input
On entry: the maximum number of steps to be attempted during one call to the integrator after which it will return with ${\mathbf{ifail}}={\mathbf{2}}$ (see d02ncf). Set ${\mathbf{maxstp}}=0$ if this option is not required. Set ${\mathbf{maxstp}}<0$ if the current value of maxstp is not to be changed.
7: $\mathbf{mxhnil}$Integer Input
On entry: the maximum number of warnings printed (if ${\mathbf{itrace}}\ge 0$, e.g., see d02nbf) per problem when $t+h=t$ on a step ($h=\text{​ current step size}$). If ${\mathbf{mxhnil}}\le 0$, a default value of $10$ is assumed.
8: $\mathbf{rwork}\left(50+4×{\mathbf{neqmax}}\right)$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: $\mathbf{ifail}$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 $-\mathbf{1}$ 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).

## 6Error Indicators and Warnings

If on entry ${\mathbf{ifail}}=0$ or $-1$, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
${\mathbf{ifail}}=1$
On entry, ${\mathbf{neqmax}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{neqmax}}\ge 1$.
${\mathbf{ifail}}=-99$
See Section 7 in the Introduction to the NAG Library FL Interface for further information.
${\mathbf{ifail}}=-399$
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.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.

Not applicable.