On Thu, Dec 09, 2010 at 07:43:52PM -0800, bluesky wrote: > > I just contect R,and still learn how to write the code. > I have a problem with argmin sum d(pi,p)/n > for example I have 3 points (a1,b1)(a2,b2)(a3,b3) ,then I want to find > p(x,y) make sure that > (sqrt((a1-x)^2+(b1-y)^2)+sqrt((a2-x)^2+(b2-y)^2)+sqrt((a3-x)^2+(b3-y)^2))/3 > is the minimum.
The following code solves the example as i understand it. # rows of matrix "a" are three points in the plane a <- rbind( c(1, 1), c(2.3, 1), c(3, 3)) d <- function(x, a) mean(sqrt(rowSums((a - rep(x, each=nrow(a)))^2))) xinit <- colMeans(a) x <- optim(xinit, d, a=a)$par plot(a) points(rbind(x), col=2) Is this, what you mean? Function optim() has further parameters, which influence efficiency and accuracy, and there are also other optimization functions. Petr Savicky. ______________________________________________ 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.
