I am trying to simulate a self avoiding random walk in 2d of length 100. So I am using two vectors of length 100 to encode the x and y coordinates. At each step I want apply a orthogonal transformation at a random point and then check to see if the walk intersects with itself. This amounts to simply checking to see if any of the ordered pairs of (x,y) coordinates in 1:j are repeated in j+1:100. This seems like it should be really easy. But I cannot find a simple method. I have been calling the pivoted portion of the walk (xn[],yn[]) for(i in 1:j) for(m in {j+1}:100) if(xn[m]==x[i]) if(yn[m]==y[i]) dont_transform=1 else dont_transform=0 if(dont_transform==0) for(g in j:100) {x[g]=xn[g] ; y[g]=yn[g]} z=c(x,y) dim(z)=c(100,2) z maybe the right solution would be to use intersection() but I couldnt figure out how to make it work. Any advice would be appreciated. Thanks Seth Latimer -- View this message in context: http://www.nabble.com/pivot-algorithm-tf2715472.html#a7571334 Sent from the R help mailing list archive at Nabble.com.