param.startOW {RelDists} | R Documentation |
Initial values extraction for Odd Weibull distribution
Description
This function can be used to extract initial values found with empirical
time on test transform (TTT) through initValuesOW
function.
This is used for parameter estimation in OW
distribution.
Usage
param.startOW(param, initValOW)
Arguments
param |
a character used to specify the parameter required. It can take the
values |
initValOW |
an |
Details
This function just gets initial values computed with initValuesOW
for OW
family. It must be called in sigma.start
and nu.start
arguments from gamlss
function. This function is useful only
if user want to set start values automatically with TTT plot.
See example for an illustration.
Value
A length-one vector numeric value corresponding to the initial value of the
parameter specified in param
extracted from a initValuesOW
object specified in the initValOW
input argument.
Author(s)
Jaime Mosquera GutiƩrrez jmosquerag@unal.edu.co
Examples
# Random data generation (OW distributed)
y <- rOW(n=500, mu=0.05, sigma=0.6, nu=2)
# Initial values with TTT plot
iv <- initValuesOW(formula = y ~ 1)
summary(iv)
# This data is from unimodal hazard
# See TTT estimate from sample
plot(iv, legend_options=list(pos=1.03))
# See the true hazard
curve(hOW(x, mu=0.05, sigma=0.6, nu=2), to=100, lwd=3, ylab="h(x)")
# Finally, we fit the model
require(gamlss)
con.out <- gamlss.control(n.cyc = 300, trace = FALSE)
con.in <- glim.control(cyc = 300)
(sigma.start <- param.startOW("sigma", iv))
(nu.start <- param.startOW("nu", iv))
mod <- gamlss(y~1, sigma.fo=~1, nu.fo=~1, control=con.out, i.control=con.in,
family=myOW_region(OW(sigma.link="identity", nu.link="identity"),
valid.values="auto", iv),
sigma.start=sigma.start, nu.start=nu.start)
# Estimates are close to actual values
(mu <- exp(coef(mod, what = "mu")))
(sigma <- coef(mod, what = "sigma"))
(nu <- coef(mod, what = "nu"))