NAG Library Routine Document

g13fbf  (uni_garch_asym1_forecast)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:     $\mathbf{num}$ – IntegerInput

On entry: the number of terms in the arrays ht and et from the modelled sequence.

Constraint: $\max \left(\mathbf{ip},\mathbf{iq}\right)\le \mathbf{num}$.

2:     $\mathbf{nt}$ – IntegerInput

On entry: $\xi$, the forecast horizon.

Constraint: $\mathbf{nt}>0$.

3:     $\mathbf{ip}$ – IntegerInput

On entry: the number of coefficients, ${\beta }_{\mathit{i}}$, for $\mathit{i}=1,2,\dots ,p$.

Constraints:

• $\max \left(\mathbf{ip},\mathbf{iq}\right)\le 20$;
• $\mathbf{ip}\ge 0$.

4:     $\mathbf{iq}$ – IntegerInput

On entry: the number of coefficients, ${\alpha }_{\mathit{i}}$, for $\mathit{i}=1,2,\dots ,q$.

Constraints:

• $\max \left(\mathbf{ip},\mathbf{iq}\right)\le 20$;
• $\mathbf{iq}\ge 1$.

5:     $\mathbf{theta}\left(\mathbf{iq}+\mathbf{ip}+1\right)$ – Real (Kind=nag_wp) arrayInput

On entry: the first element must contain the coefficient ${\alpha }_o$ and the next iq elements must contain the coefficients ${\alpha }_{\mathit{i}}$, for $\mathit{i}=1,2,\dots ,q$. The remaining ip elements must contain the coefficients ${\beta }_{\mathit{j}}$, for $\mathit{j}=1,2,\dots ,p$.

6:     $\mathbf{gamma}$ – Real (Kind=nag_wp)Input

On entry: the asymmetry parameter $\gamma$ for the $\text{GARCH}\left(p,q\right)$ sequence.

7:     $\mathbf{fht}\left(\mathbf{nt}\right)$ – Real (Kind=nag_wp) arrayOutput

On exit: the forecast values of the conditional variance, $h_t$, for $\mathit{t}=T+1,\dots ,T+\xi$.

8:     $\mathbf{ht}\left(\mathbf{num}\right)$ – Real (Kind=nag_wp) arrayInput

On entry: the sequence of past conditional variances for the $\text{GARCH}\left(p,q\right)$ process, $h_{\mathit{t}}$, for $\mathit{t}=1,2,\dots ,T$.

9:     $\mathbf{et}\left(\mathbf{num}\right)$ – Real (Kind=nag_wp) arrayInput

On entry: the sequence of past residuals for the $\text{GARCH}\left(p,q\right)$ process, ${\epsilon }_{\mathit{t}}$, for $\mathit{t}=1,2,\dots ,T$.

10:   $\mathbf{ifail}$ – IntegerInput/Output

On entry: ifail must be set to $0$, $-1\text{ or }1$. If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation 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 argument, 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

$\mathbf{ifail}=1$

On entry,	$\mathbf{num}<\max \left(\mathbf{ip},\mathbf{iq}\right)$,
or	$\mathbf{iq}<1$,
or	$\mathbf{ip}<0$,
or	$\max \left(\mathbf{ip},\mathbf{iq}\right)>20$,
or	$\mathbf{nt}\le 0$.

$\mathbf{ifail}=-99$

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

See Section 3.9 in How to Use the NAG Library and its Documentation for further information.

$\mathbf{ifail}=-399$

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

See Section 3.8 in How to Use the NAG Library and its Documentation for further information.

$\mathbf{ifail}=-999$

Dynamic memory allocation failed.

See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example