Thank you both... I think that was what I was looking for. If not, I'll be back ;-) I can't plot it though? The reason that I don't want to use if-statements is because I'm using a package that can't take if. The package is programmed by some people at the University of Southern Denmark.

The piecewise page? I don't understand? what and where is that? ---------------------- My wish, is simplified: To assign af function V(x) which has the property to take the value infinity for all x<0, and takes the values a*x for all x>0. Without using if-statements. -----------------------------