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gamlss.dist (version 4.3-4)

SEP: The Skew Power exponential (SEP) distribution for fitting a GAMLSS

Description

This function defines the Skew Power exponential (SEP) distribution, a four parameter distribution, for a gamlss.family object to be used for a GAMLSS fitting using the function gamlss(). The functions dSEP, pSEP, qSEP and rSEP define the density, distribution function, quantile function and random generation for the Skew Power exponential (SEP) distribution.

Usage

SEP(mu.link = "identity", sigma.link = "log", nu.link = "identity", 
    tau.link = "log")
dSEP(x, mu = 0, sigma = 1, nu = 0, tau = 2, log = FALSE)
pSEP(q, mu = 0, sigma = 1, nu = 0, tau = 2, lower.tail = TRUE, 
     log.p = FALSE)
qSEP(p, mu = 0, sigma = 1, nu = 0, tau = 2, lower.tail = TRUE, 
     log.p = FALSE, lower.limit = mu - 5 * sigma, 
     upper.limit = mu + 5 * sigma)
rSEP(n, mu = 0, sigma = 1, nu = 0, tau = 2)

Arguments

mu.link
Defines the mu.link, with "identity" link as the default for the mu parameter. Other links are "$1/mu^2$" and "log"
sigma.link
Defines the sigma.link, with "log" link as the default for the sigma parameter. Other links are "inverse" and "identity"
nu.link
Defines the nu.link, with "identity" link as the default for the nu parameter. Other links are "$1/nu^2$" and "log"
tau.link
Defines the tau.link, with "log" link as the default for the tau parameter. Other links are "$1/tau^2$", and "identity
x,q
vector of quantiles
mu
vector of location parameter values
sigma
vector of scale parameter values
nu
vector of skewness nu parameter values
tau
vector of kurtosis tau parameter values
log, log.p
logical; if TRUE, probabilities p are given as log(p).
lower.tail
logical; if TRUE (default), probabilities are P[X <= x],="" otherwise,="" p[x=""> x]
p
vector of probabilities.
n
number of observations. If length(n) > 1, the length is taken to be the number required
lower.limit
lower limit for the golden search to find quantiles from probabilities
upper.limit
upper limit for the golden search to find quantiles from probabilities

Value

  • SEP() returns a gamlss.family object which can be used to fit the SEP distribution in the gamlss() function. dSEP() gives the density, pSEP() gives the distribution function, qSEP() gives the quantile function, and rSEP() generates random deviates.

Warning

The qSEP and rSEP are slow since they are relying on golden section for finding the quantiles

Details

The probability density function of the Skew Power exponential distribution, (SEP), is defined as $$f(y|n,\mu,\sigma\,\nu,\tau)==\frac{z}{\sigma} \Phi(\omega) \hspace{1mm} f_{EP}(z,0,1,\tau)$$ for $-\infty < y < \infty$, $\mu=(-\infty,+\infty)$, $\sigma>0$, $\nu=(-\infty,+\infty)$ and $\tau>0$. where $z = \frac{y-\mu}{\sigma}$, $\omega = sign(z)|z|^{\tau/2}\nu \sqrt{2/\tau}$ and $f_{EP}(z,0,1,\tau)$ is the pdf of an Exponential Power distribution.

References

Diciccio, T. J. and Mondi A. C. (2004). Inferential Aspects of the Skew Exponential Power distribution., JASA, 99, 439-450. Rigby, R. A. and Stasinopoulos D. M. (2005). Generalized additive models for location, scale and shape,(with discussion), Appl. Statist., 54, part 3, pp 507-554. Stasinopoulos D. M. Rigby R. A. and Akantziliotou C. (2006) Instructions on how to use the GAMLSS package in R. Accompanying documentation in the current GAMLSS help files, (see also http://www.gamlss.org/). Stasinopoulos D. M. Rigby R.A. (2007) Generalized additive models for location scale and shape (GAMLSS) in R. Journal of Statistical Software, Vol. 23, Issue 7, Dec 2007, http://www.jstatsoft.org/v23/i07.

See Also

gamlss.family, JSU, BCT

Examples

Run this code
SEP()   # 
plot(function(x)dSEP(x, mu=0,sigma=1, nu=1, tau=2), -5, 5, 
 main = "The SEP  density mu=0,sigma=1,nu=1, tau=2")
plot(function(x) pSEP(x, mu=0,sigma=1,nu=1, tau=2), -5, 5, 
 main = "The BCPE  cdf mu=0, sigma=1, nu=1, tau=2")
dat <- rSEP(100,mu=10,sigma=1,nu=-1,tau=1.5)
# library(gamlss)
# gamlss(dat~1,family=SEP, control=gamlss.control(n.cyc=30))

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