Thanks to Martin Sandiford, I can draw a graph using lower diagonal type of data. One problem I can't solve is to put appropriate tick marks on the graph ############################################## x<- matrix(NA,50,50) x[lower.tri(x)] <- runif(choose(50,2),0,1) plot(1,2,xlim=c(1,50),ylim=c(49,2),xlab="",ylab="",type="n") par(new=T) image(1-t(x)[,ncol(x):1], col=gray.colors(100), axes=FALSE) ############################################## I like ticks on both x-axis and y-axis to be located in the middle of each cell. X-axis needs to start with 1 and end with 50. Y-axis needs to start with 2 and end with 49. I looked at the help file for "par" and changed some settings but I couldn't succeed. Any advice on this issue would be greatly appreciated !! TM _________________________________________________________________ Don’t just search. Find. Check out the new MSN Search!