NAG Library Routine Document

D02QZF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     $\mathrm{NEQF}$ – INTEGERInput

On entry: the number of first-order ordinary differential equations being solved by the integration routine. It must contain the same value as the parameter NEQF in a prior call to the setup routine D02QWF.

2:     $\mathrm{TWANT}$ – REAL (KIND=nag_wp)Input

On entry: the point at which components of the solution and derivative are to be evaluated. TWANT should not normally be an extrapolation point, that is TWANT should satisfy

• $\mathit{told}\le \mathbf{TWANT}\le \mathrm{T}$,

or if integration is proceeding in the negative direction

• $\mathit{told}\ge \mathbf{TWANT}\ge \mathrm{T}$,

where $\mathit{told}$ is the previous integration point and is, to within rounding, TCURR – HLAST (see D02QXF). Extrapolation is permitted but not recommended and $\mathbf{IFAIL}=\mathbf{2}$ is returned whenever extrapolation is attempted.

3:     $\mathrm{NWANT}$ – INTEGERInput

On entry: the number of components of the solution and derivative whose values at TWANT are required. The first NWANT components are evaluated.

Constraint: $1\le \mathbf{NWANT}\le \mathbf{NEQF}$.

4:     $\mathrm{YWANT}\left(\mathbf{NWANT}\right)$ – REAL (KIND=nag_wp) arrayOutput

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

5:     $\mathrm{YPWANT}\left(\mathbf{NWANT}\right)$ – REAL (KIND=nag_wp) arrayOutput

On exit: the calculated value of the $\mathit{i}$th component of the derivative at TWANT, for $\mathit{i}=1,2,\dots ,\mathbf{NWANT}$.

6:     $\mathrm{RWORK}\left(\mathbf{LRWORK}\right)$ – REAL (KIND=nag_wp) arrayCommunication Array

On entry: this must be the same parameter RWORK as supplied to D02QWF and to D02QFF or D02QGF. It is used to pass information from these routines to D02QZF. Therefore its contents must not be changed before a call to D02QZF.

7:     $\mathrm{LRWORK}$ – INTEGERInput

On entry: the dimension of the array RWORK as declared in the (sub)program from which D02QZF is called.

This must be the same parameter LRWORK as supplied to D02QWF.

8:     $\mathrm{IWORK}\left(\mathbf{LIWORK}\right)$ – INTEGER arrayCommunication Array

On entry: this must be the same parameter IWORK as supplied to D02QWF and to D02QFF or D02QGF. It is used to pass information from these routines to D02QZF. Therefore its contents must not be changed before a call to D02QZF.

9:     $\mathrm{LIWORK}$ – INTEGERInput

On entry: the dimension of the array IWORK as declared in the (sub)program from which D02QZF is called.

This must be the same parameter LIWORK as supplied to D02QWF.

10:   $\mathrm{IFAIL}$ – 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

$\mathbf{IFAIL}=1$

An integration routine (D02QFF or D02QGF) has not been called, no integration steps have been taken since the last call to D02QWF with $\mathbf{STATEF}=\text{'S'}$, one or more of the parameters LRWORK, LIWORK and NEQF does not match the same parameter supplied to D02QWF, or NWANT does not satisfy $1\le \mathbf{NWANT}\le \mathbf{NEQF}$.

$\mathbf{IFAIL}=2$

D02QZF has been called for extrapolation. The values of the solution and its derivative at TWANT have been calculated and placed in YWANT and YPWANT before returning with this warning (see Section 7).

$\mathbf{IFAIL}=-99$

An unexpected error has been triggered by this routine. Please contact NAG.

See Section 3.8 in the Essential Introduction for further information.

$\mathbf{IFAIL}=-399$

Your licence key may have expired or may not have been installed correctly.

See Section 3.7 in the Essential Introduction for further information.

$\mathbf{IFAIL}=-999$

Dynamic memory allocation failed.

See Section 3.6 in the Essential Introduction for further information.

7  Accuracy

8  Parallelism and Performance

9  Further Comments

10  Example

10.1  Program Text

Program Text (d02qzfe.f90)

10.2  Program Data

Program Data (d02qzfe.d)

10.3  Program Results

Program Results (d02qzfe.r)