garchSpec {fGarch}R Documentation

Univariate GARCH Time Series Specification

Description

Specifies an univariate GARCH time series model.

Usage

garchSpec(model = list(omega = 1.0e-6, alpha = 0.1, beta = 0.8), 
    presample = NULL, cond.dist = c("rnorm", "rged", "rstd", "rsnorm", 
    "rsged", "rsstd"), rseed = NULL)
    
show.garchSpec(object)

Arguments

cond.dist a character string naming the desired conditional distribution. Valid values are "dnorm", "dged", "dstd", "dsnorm", "dsged", "dsstd". The default value is the normal distribution.
model a list of GARCH model parameters:
omega - the constant coefficient of the variance equation, by default 1e-6;
alpha - the value or vector of autoregressive coefficients, by default 0.1, specifying a model of order 1;
beta - the value or vector of variance coefficients, by default 0.8, specifying a model of order 1;
The optional values for the linear part are:
mu - the mean value, by default 0;
ar - the autoregressive ARMA coefficients, by default 0;
ma - the moving average ARMA coefficients, by default 0.
The optional parameters for the conditional distributions are:
skew - the skewness parameter (also named xi), by default 0.9, effective only for the "dsnorm", the "dsged", and the "dsstd" skewed conditional distributions;
shape = the shape parameter (also named nu), by default 2 for the "dged" and "dsged", and by default 4 for the "dstd" and "dsstd" conditional distributions.

Note, the default model specifies Bollerslev's GARCH(1,1) model with normal distributed innovations.
object an object of class garchSpec as returned from the function garchSpec().
presample a numeric three column matrix with start values for the series, for the innovations, and for the conditional variances. For an ARMA(m,n)-GARCH(p,q) process the number of rows must be at least max(m,n,p,q), longer presamples are cutted.
rseed single integer argument, the seed for the intitialization of the random number generator for the innovations.

Value

garchSpec

returns a S4 object of class garchSpec with the following slots:

@call the call of the garch function.
@formula a list with two formula entries for the mean and variance equation.
@model a list with the model parameters.
@presample a numeric matrix with presample values.
@distribution a character string with the name of the conditional distribution.
@rseed an integer with the random number generator seed.

Author(s)

Diethelm Wuertz for the Rmetrics R-port.

Examples

## garchSpec -

   # Normal Conditional Distribution:
   spec = garchSpec()
   spec
   
   # Skewed Normal Conditional Distribution:
   spec = garchSpec(model = list(skew = 0.8), cond.dist = "rsnorm")
   spec
   
   # Skewed GED Conditional Distribution:
   spec = garchSpec(model = list(skew = 0.9, shape = 4.8), cond.dist = "rsged")
   spec

[Package fGarch version 260.72 Index]