[EMAIL PROTECTED] wrote in news:[EMAIL PROTECTED]:
> Hi, I am fairly new to R, and am stuck. Please use an informative subject line when posting. (And read the Posting Guide. <http://www.R-project.org/posting-guide.html> > I want to write an R function with argument n that returns a vector > of length n with n simulated observations from the double > exponential distribution with density: ??g(y) = 1/2e^-y I think that might be g(y) = (1/2)e^(-abs(y)). Johnson, Kotz and Balakrishnan "Cont. Univariate Distr. 2nd ed" illustrate the acceptance-rejection method for Laplace random numbers on p 154. At any rate, there is already a package that will generate the desired random numbers. help.search("double exponential") #tells you: #DExp-class(distr) Class "DExp" #so DExp is a class in the "distr" package require(distr) ?DExp ?rexp #make D a distribution argument to distr's r(), d(), and p() functions D <- DExp(rate=1) #which is the Laplace fucntion # make rvec a 100 element vector of random Dexp(rate=1) rvec<-r(D)(100) > > For the double exponential, I want to generate y~Exp(1) and then > take ?y with probability 0.5 #create 100 random binomials rprob<-rbinom(100,1,0.5) head(rprob) #[1] 0 0 1 0 1 0 onehalf<-rvec*rprob head(onehalf) #0.0000000 0.0000000 0.6638434 0.0000000 0.4638312 0.0000000 Or if you didn't want the extraneous zeros as placeholders you could strip them out with: onehalf[onehalf != 0] #[1] 0.663843413 0.463831152 2.586626569 1.227912636 3.860839987 # -3.394600764 0.542588566 <snip> Note: this does not give you 50 elements every time. ______________________________________________ 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.
