I'm trying to solve a non-linear partial differential equation, using NDSolve. Mathematica gives the solution as an interpolating function. As I vary a parameter in the initial equation, I get new solutions, which are all similar, and my aim is that by varying my parameters I will eventually find one solution satisfying my criteria. All this is ok, my problem is that the interpolating functions exist only over a finite domain, and that domain changes from solution to solution. I want to be able to test my solution at a certain domain value, but I do NOT want mathematica to extrapolate a value if one does not already exist, I need to ignore these solutions.... so... any ideas on how to either extract the upper limit of the domain, or tell mathematica not to extrapolate?