At a guess ... > erfc <- function(x) 2 * pnorm(x * sqrt(2), lower = FALSE) > erfcinv <- function(x) qnorm(x/2, lower = FALSE)/sqrt(2) > erfc(0.3) [1] 0.6713732 > erfcinv(erfc(0.3)) [1] 0.3 >
It may not hurt to include these wrappers in R for matlab refugees. They seem to be coming thick and fast these days. Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: +61 4 8819 4402 Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] http://www.cmis.csiro.au/bill.venables/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of sun Sent: Monday, 14 April 2008 8:50 AM To: [EMAIL PROTECTED] Subject: Re: [R] R equivalent of erfcinv in matlab Peter Dalgaard wrote: > sun wrote: >> I am converting some matlab code into R that use inverse of the >> complementary error function, erfcinv and did not find an equivalent in >> R, is there such a function in some contributed modules? >> >> > Basically, it is qnorm() with suitable scaling. The help page for Normal > has the construction for erfc() from pnorm() so just solve erfc(x) = y > for x. > Thanks for your quick answer and useful information! But please forgive my ignorance, I do not really know how to solve this inverse function actually. for example, >erfc <- function(x) 2 * pnorm(x * sqrt(2), lower = FALSE) > erfc(0.3) [1] 0.6713732 How do I find 0.3 given 0.6713732? Thanks! ______________________________________________ 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.
