Not sure if there's a pre-defined function for it, but use your basic math skills: the normal distribution is
dnorm(x) = 1/(sqrt(2*pi)) * exp(-x^2/2), so the inverse function (on the interval [0, infinity] is f = function(x) {sqrt( -2*log(sqrt(2*pi) * x)) } Since the dnorm function is not 1-to-1, f is strictly speaking not the inverse (since the latter doesn't exist), but it is true that f(dnorm(x)) = abs(x). Test: x = seq(from = -2, to = 2, by = 0.01) plot(x, dnorm(x)) plot(x, f(dnorm(x))) > all.equal(abs(x), f(dnorm(x))) [1] TRUE Note again that f(dnorm(x)) = abs(x), not x, since the dnorm function is not 1-to-1. Peter On Fri, Nov 12, 2010 at 2:35 PM, Edwin Sun <c...@cfr.msstate.edu> wrote: > > Hello all, > > I have a question about basic statistics. Given a PDF value of 0.328161, > how can I find out the value of -0.625 in R? It is like reversing the dnorm > function but I do not know how to do it in R. > >> pdf.xb <- dnorm(-0.625) > >> pdf.xb > [1] 0.328161 > >> qnorm(pdf.xb) > [1] -0.444997 > >> pnorm(pdf.xb) > [1] 0.628605 > > Many thanks, > > > Edwin > > > -- > View this message in context: > http://r.789695.n4.nabble.com/dnorm-and-qnorm-tp3040427p3040427.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > 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. > ______________________________________________ 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.