NAG FL Interface
d02pjf (ivp_​rk_​interp_​eval)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{icheck}$ – Integer Input

On entry: indicates whether consistency checks on input arguments should be performed

$\mathbf{icheck}\ne 1$

Don't perform checks on input arguments.

$\mathbf{icheck}=1$

Perform consistency checks on input arguments.

It is recommended to use $\mathbf{icheck}=1$ on the first call following a call to d02phf and to set $\mathbf{icheck}\ne 1$ on subsequent calls within the last step to avoid the overhead of argument checking.

2: $\mathbf{n}$ – Integer Input

On entry: $n$, the dimension of the system of ODEs being integrated.

Constraint: this must be the same value as supplied in a previous call to d02pqf.

3: $\mathbf{nwant}$ – Integer Input

On entry: only the first nwant system components to be computed. This should be the same value as passed to d02phf when computing the interpolant.

Constraint: $\mathbf{nwant}=\mathbf{nwant}$ passed to d02phf.

4: $\mathbf{t}$ – Real (Kind=nag_wp) Input

On entry: $t$, the value of the independent variable where a solution is desired. Although any value of $t$ can be supplied, accurate solutions can only be obtained for values in the range of the last time-step taken by d02pgf.

5: $\mathbf{ideriv}$ – Integer Input

On entry:

$\mathbf{ideriv}=0$

Compute approximations to the first nwant components of the solution $y\left(t\right)$.

$\mathbf{ideriv}=1$

Compute approximations to the first nwant components of the first derivatives of the solution $y^{\prime }\left(t\right)$.

Constraint: $\mathbf{ideriv}=0$ or $1$.

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

On exit:

$\mathbf{ideriv}=0$

The first nwant components of the solution $y\left(t\right)$.

$\mathbf{ideriv}=1$

The first nwant components of the first derivatives of the solution $y^{\prime }\left(t\right)$.

7: $\mathbf{wcomm}\left(\mathbf{lwcomm}\right)$ – Real (Kind=nag_wp) array Communication Array

On entry: this must be the same array supplied in a previous call to d02phf. It must remain unchanged between calls.

8: $\mathbf{lwcomm}$ – Integer Input

On entry: length of wcomm. This should be the same value as supplied in a previous call to d02phf.

If in a previous call to d02pqf:

• $\mathbf{method}=1$ or $\mathrm{-1}$, lwcomm must be at least $1$.
• $\mathbf{method}=2$ or $\mathrm{-2}$, lwcomm must be at least $\mathbf{n}+\max (\mathbf{n},5\times \mathbf{nwant})$.
• $\mathbf{method}=3$ or $\mathrm{-3}$, $\mathbf{lwcomm}\ge 8\times \mathbf{nwant}$.

9: $\mathbf{iwsav}\left(130\right)$ – Integer array Communication Array

10: $\mathbf{rwsav}\left(32\times \mathbf{n}+350\right)$ – Real (Kind=nag_wp) array Communication Array

On entry: these must be the same arrays supplied in a previous call d02pgf. They must remain unchanged between calls.

On exit: information about the integration for use on subsequent calls to d02pgf, d02phf or other associated routines.

11: $\mathbf{ifail}$ – Integer Input/Output

On entry: ifail must be set to $0$, $\mathrm{-1}$ 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 $\mathrm{-1}$ means that an error message is printed while a value of $1$ means that it is not.

If halting is not appropriate, the value $\mathrm{-1}$ 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).

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.

On entry, $\mathbf{ideriv}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{ideriv}=0$ or $1$.

On entry, $\mathbf{lwcomm}=⟨\mathit{\text{value}}⟩$, $\mathbf{n}=⟨\mathit{\text{value}}⟩$ and $\mathbf{nwant}=⟨\mathit{\text{value}}⟩$.
Constraint: for $\mathbf{method}=\mathrm{-2}$ or $2$, $\mathbf{lwcomm}\ge \mathbf{n}+\max (\mathbf{n},5\times \mathbf{nwant})$.

On entry, $\mathbf{lwcomm}=⟨\mathit{\text{value}}⟩$.
Constraint: for $\mathbf{method}=\mathrm{-1}$ or $1$, $\mathbf{lwcomm}\ge 1$.

On entry, $\mathbf{lwcomm}=⟨\mathit{\text{value}}⟩$ and $\mathbf{nwant}=⟨\mathit{\text{value}}⟩$.
Constraint: for $\mathbf{method}=\mathrm{-3}$ or $3$, $\mathbf{lwcomm}\ge 8\times \mathbf{nwant}$.

On entry, $\mathbf{n}=⟨\mathit{\text{value}}⟩$, but the value passed to the setup routine was $\mathbf{n}=⟨\mathit{\text{value}}⟩$.

On entry, $\mathbf{nwant}=⟨\mathit{\text{value}}⟩$, but on interpolation setup $\mathbf{nwant}=⟨\mathit{\text{value}}⟩$.
Constraint: nwant must be unchanged from setup.

The previous call to the interpolation setup routine returned an error.

You cannot call this routine before you have called the interpolation setup.

$\mathbf{ifail}=-99$

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