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Maximum likelihood estimation of the degrees of freedom for a chi-squared distribution. Also fits the chi distribution.
chisq(link = "loglink", zero = NULL, squared = TRUE)An object of class "vglmff"
(see vglmff-class).
The object is used by modelling functions
such as vglm,
and vgam.
See CommonVGAMffArguments for
information.
Logical.
Set FALSE for the chi distribution.
T. W. Yee
The degrees of freedom is treated as a real parameter to be estimated and not as an integer. Being positive, a log link is used by default. Fisher scoring is used.
If a random variable has a chi-squared distribution then the square root of the random variable has a chi distribution. For both distributions, the fitted value is the mean.
Forbes, C., Evans, M., Hastings, N. and Peacock, B. (2011). Statistical Distributions, Hoboken, NJ, USA: John Wiley and Sons, Fourth edition.
Chisquare.
uninormal.
cdata <- data.frame(x2 = runif(nn <- 1000))
cdata <- transform(cdata, y1 = rchisq(nn, df = exp(1 - 1 * x2)),
y2 = rchisq(nn, df = exp(2 - 2 * x2)))
fit <- vglm(cbind(y1, y2) ~ x2, chisq, data = cdata, trace = TRUE)
coef(fit, matrix = TRUE)
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