[EMAIL PROTECTED] wrote:
> > sddist
>>> > >>
> > function(s,n) {
> > sig2 <- n*s*s/(n-1)
> > 2*(n/(2*sig2))^((n-1)/2) / gamma((n-1)/2) * exp(-n*s*s/(2*sig2)) *
s^(n-2)
> > }There is another way using more statistical knowledge: Building on functions already available in R one may note that the easiest way of defining sddist is sddist<-function(s,n) dchisq(n*s^2,n-1)*2*n*s Plotting this function for n in seq(2,12,2) reproduces the graph in Mathworld. The idea is the following: given a random variable x with a chisquare distribution with df n-1, s can be defined by s=sqrt(x/n) and therefore x=n*s^2 If F and G are the cumulative distribution functions of x and s and f and g are the density functions of x and s, then we have G(s)=F(n*s^2) and therefore g(s)=f(n*s^2)*2*n*s -- Erich Neuwirth, University of Vienna Faculty of Computer Science Computer Supported Didactics Working Group Visit our SunSITE at http://sunsite.univie.ac.at Phone: +43-1-4277-39464 Fax: +43-1-4277-39459 ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
