R: Change Parameterizations of the Variance Gamma Distribution
vgChangePars
R Documentation
Change Parameterizations of the Variance Gamma Distribution
Description
This function interchanges between the following 4 parameterizations
of the variance gamma distribution:
1. c, sigma, theta, nu
2. theta, sigma, mu, tau
3. theta, sigma, kappa, tau
4. lambda, alpha, beta, mu
The first set of parameterizations is given in Seneta (2004). The second and
third ones are the parameterizations given in Kotz et al. (2001). The
last set takes the form of the generalized hyperbolic distribution
parameterization. delta is not included since the
variance gamma distribution is a limiting case of generalized
hyperbolic distribution with delta always equal to 0.
Usage
vgChangePars(from, to, param, noNames = FALSE)
Arguments
from
The set of parameters to change from.
to
The set of parameters to change to.
param
"from" parameter vector consisting of 4 numerical elements.
noNames
Logical. When TRUE, suppresses the parameter
names in the output.
Details
In the 3 parameterizations, the following must be positive:
1. sigma, nu
2. sigma, tau
3. sigma, tau
4. lambda, alpha
In addition in the 4th parameterization, the absolute value of
beta must be less than alpha.
Value
A numerical vector of length 4 representing param in the
to parameterization.
Seneta, E. (2004). Fitting the variance-gamma model to financial data.
J. Appl. Prob., 41A:177–187.
Kotz, S, Kozubowski, T. J., and Podg<c3><b3>rski,
K. (2001).
The Laplace Distribution and Generalizations. Birkhauser,
Boston, 349 p.
See Also
dvg, vgMom
Examples
param1 <- c(2,2,1,3) # Parameterization 1
param2 <- vgChangePars(1, 2, param1) # Convert to parameterization 2
param2 # Parameterization 2
vgChangePars(2, 1, as.numeric(param2)) # Convert back to parameterization 1
param3 <- c(1,2,0,0.5) # Parameterization 3
param1 <- vgChangePars(3, 1, param3) # Convert to parameterization 1
param1 # Parameterization 1
vgChangePars(1, 3, as.numeric(param1)) # Convert back to parameterization 3