Hi there. Thanks for your time in advance. My final goal is to calculate 1/2*integral of (f1(x)^1/2-f2(x)^(1/2))^2dx (Latex codes: $\frac{1}{2}\int^{{\infty}}_{\infty} (\sqrt{f_1(x)}-\sqrt{f_2(x)})^2dx $.) where f1(x) and f2(x) are two marginal densities. My problem: I have the following R codes using "adapt" package. Although "adapt" function is mainly designed for more than 2 dimensions, the manual says it will also call up "integrate" if the number of dimension equals one. I feed in the data x1 and x2 and bandwidths h1 and h2. These codes worked well when my final goal was to take double integrals. integrand <- function(x) { # x input is evaluation point for x1 and x2, a 2x1 vector x1.eval <- x[1] x2.eval <- x[2] # n is the number of observations n <- length(x1) # x1 and x2 are the vectors read from data.dat # Compute the marginal densities f.x1 <- sum(dnorm((x1.eval-x1)/h1))/(n*h1) f.x2 <- sum(dnorm((x2.eval-x2)/h2))/(n*h2) # Return the integrand # return((sqrt(f.x1)-sqrt(f.x2))**2) } estimate<-0.5*adapt(1, lo=lo.default, up=up.default, minpts=minpts.default, maxpts=maxpts.default, functn=integrand, eps=eps.default, x1, x2,h1,h2)$value But when I used it for one-dimension, it failed. Some of my colleagues suggested getting rid of "x2.eval" in the "integrand" because it is only one integral. But after I changed it, it still didn't work. R gave the error msg: "evaluation of function gave a result of wrong length" I am not a frequent R user..although I looked up the mailing list for a while and there were few postings asking similar questions, I can't still figure out why my codes won't work. Any help will be appreciated.