[R] distances between points in R^3

From: baptiste Auguié <ba208_at_exeter.ac.uk>
Date: Sun, 3 Feb 2008 18:55:30 +0000


Dear R helpers,

I'm trying to write a numerical scheme for a boundary integral method to solve an electromagnetic problem. This requires the computation of the distance between points at the surface of an object (a sphere, in my example). Here is my code,

> require(rgl)
> r<-1
> size<-10
> theta<-seq(0,2*pi,length=size*2)
> phi<-seq(0,pi,length=size)
> pc = as.matrix(rbind(expand.grid(theta,phi)))
> x<- r* sin(pc[,2]) * cos(pc[,1])
> y<- r* sin(pc[,2]) * sin(pc[,1])
> z<- r* cos(pc[,2])
>
> plot3d(x, y, z, col=rainbow(1000), size=2,zlim=c(-1,1)) #
> scatterplot of points on a sphere
>
> df<- unique(rbind(x,y,z), MARGIN = 2 ) # removes duplicates in
> cartesian coordinates
> dimension <- dim(df)[1]
> matDistances <- array(data=0,dim=c(dimension,dimension))
>
> norm <- function(a) sqrt(a %*% a)
>
> for (ii in 1:dimension){
> for (jj in ii:dimension){
> matDistances[ii,jj]<- norm( df[,ii] - df[,jj])
> }
> }

This is both inefficient and ugly, I'll welcome any suggestion. In particular:

Many thanks in advance,

baptiste


Baptiste Auguié

Physics Department
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag
http://projects.ex.ac.uk/atto



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