Dear Dr. Dalgaard, Thank you for your insight! In fact, I did read the example documentation, however, it pretty much told me the same thing that my little simulation did: there is ALOT of point mass at zero.
Is there any fix to this problem? Seeing that rgamma won't work accurately, if I wanted to plot a density of an inverse gamma distribution with small scale and shape parameters, how would I do so? Peter Dalgaard <[EMAIL PROTECTED]> wrote: Gregory Gentlemen wrote: > Hello fellow R users, > > I wanted to view the density on the standard deviation scale of a > gamma(0.001, 0.001) prior for the precision. I did this as seen in the code > below and found that for some reason rgamma is giving many values equal to > zero, which is strange since a gamma distribution is continuous. What is > going on here? > > Thanks for any help in advance. > Greg > That sort of shape parameter gives a distribution with most of its mass squashed against the y axis, so random numbers underflow to zero. But why did you not read the Example section of help(rgamma)? The effect is clearly indicated there. > >> x1 <- rgamma(10000, shape=0.001, scale=0.001) >> sd1 <- 1/sqrt(x1) >> truehist(sd1, xlim=c(0, 1.5)) >> > Error in truehist(sd1, xlim = c(0, 1.5)) : > 'nbins' must result in a positive integer > >> summary(sd1) >> > Min. 1st Qu. Median Mean 3rd Qu. Max. > 2.266e+01 9.311e+66 3.250e+153 Inf Inf Inf > > > > --------------------------------- > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 --------------------------------- [[alternative HTML version deleted]]
______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
