Greetings R-folk, I'll greatly appreciate any help you can offer... I can't figure out how to add the gradient vector of a function f(x,y) evaluated at a point (x1,y1) onto a contour() graph. I see that deriv(...,func=TRUE) gives a function that takes (x1,y1) and gives the correct gradient (x2,y2) as part of it's output, but I haven't been able to feed that info into an arrows(x1,y1,x1+x2,y1+y2) command. I've tried using attr(eval(deriv(...),"gradient"), but can't make it work Or is there something I've completely missed? Thanks, Tim ____________________ tim at sulser.com