NAG FL Interface
d02xjf (ivp_​stiff_​nat_​interp)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{xsol}$ – Real (Kind=nag_wp) Input

On entry: the point at which the first $m$ components of the solution are to be evaluated. xsol should not be an extrapolation point, that is xsol should satisfy $\left(\mathbf{xsol}-\mathbf{x}\right)\times \mathbf{hu}\le 0.0$. Extrapolation is permitted but not recommended.

2: $\mathbf{sol}\left(\mathbf{m}\right)$ – Real (Kind=nag_wp) array Output

On exit: the calculated value of the $\mathit{i}$th component of the solution at xsol, for $\mathit{i}=1,2,\dots ,m$.

3: $\mathbf{m}$ – Integer Input

On entry: $m$, the number of components of the solution whose values at xsol are required. The first m components are evaluated.

Constraint: $1\le \mathbf{m}\le \mathbf{neq}$.

4: $\mathbf{ysav}\left(\mathbf{ldysav},\mathbf{sdysav}\right)$ – Real (Kind=nag_wp) array Communication Array

On entry: the values provided in the argument ysav on return from the integrator.

5: $\mathbf{ldysav}$ – Integer Input

On entry: the value used for the argument ldysav when calling the integrator.

Constraint: $\mathbf{ldysav}\ge \mathbf{neq}$.

6: $\mathbf{sdysav}$ – Integer Input

On entry: the value used for the argument sdysav when calling the integrator.

Constraint: $\mathbf{sdysav}\ge \mathbf{nqu}+1$.

7: $\mathbf{neq}$ – Integer Input

On entry: the value used for the argument neq when calling the integrator.

Constraint: $1\le \mathbf{neq}$.

8: $\mathbf{x}$ – Real (Kind=nag_wp) Input

On entry: the latest value at which the solution has been computed, as provided in the argument tcur on return from the optional output d02nyf.

9: $\mathbf{nqu}$ – Integer Input

On entry: the order of the method used up to the latest value at which the solution has been computed, as provided in the argument nqu on return from the optional output d02nyf.

Constraint: $\mathbf{nqu}\ge 1$.

10: $\mathbf{hu}$ – Real (Kind=nag_wp) Input

On entry: the last successful step used, that is the step used in the integration to get to x, as provided in the argument hu on return from the optional output d02nyf.

11: $\mathbf{h}$ – Real (Kind=nag_wp) Input

On entry: the next step size to be attempted in the integration, as provided in the argument h on return from the optional output d02nyf.

12: $\mathbf{ifail}$ – 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).

If d02xjf is to be used for extrapolation, ifail must be set to $1$ before entry. It is then essential to test the value of ifail on exit for $\mathbf{ifail}=\mathbf{1}$ or $\mathbf{2}$.

6 Error Indicators and Warnings

$\mathbf{ifail}=1$

On entry, $\mathbf{ldysav}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{ldysav}\ge 1$.

On entry, $\mathbf{m}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{m}\ge 1$.

On entry, $\mathbf{m}=〈\mathit{\text{value}}〉$ and $\mathbf{neq}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{m}\le \mathbf{neq}$.

On entry, $\mathbf{neq}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{neq}\ge 1$.

On entry, $\mathbf{neq}=〈\mathit{\text{value}}〉$ and $\mathbf{ldysav}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{neq}\le \mathbf{ldysav}$.

On entry, $\mathbf{nqu}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{nqu}\ge 1$.

On entry, $\mathbf{sdysav}=〈\mathit{\text{value}}〉$ and $\mathbf{nqu}=〈\mathit{\text{value}}〉$.
Constraint: $\mathbf{sdysav}\ge \mathbf{nqu}+1$.

$\mathbf{ifail}=2$

On entry, $\mathbf{h}=0.0$.

On entry, $\mathbf{hu}=0.0$.

$\mathbf{ifail}=3$

On entry, $\mathbf{xsol}=〈\mathit{\text{value}}〉$, $\mathbf{x}=〈\mathit{\text{value}}〉$ and $\mathbf{h}=〈\mathit{\text{value}}〉$.
Constraint: xsol should not be an extrapolation point.

$\mathbf{ifail}=-99$

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.

$\mathbf{ifail}=-399$

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.

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example