I have a program that randomly generates line plots and what I would like to do now is compare two of those line plots and get a measure of 'similarity' between them. Now I feel as if this measure of similarity is relative to other measures I'm taking; correct me if I'm wrong. So is there any theorem/algorithm that can do this? If not, any that will get me closer to what I want?
You could check section 14.7 of Numerical Recipes on whether two two-dimensional distributions differ. Obsolete versions are free.