Hi Jacob, Thanks for the code segments. You have made some good progress, although I do see some problems with what you are doing. Recall: GOLDEN RULE 3 of programming -- "It always saves time in the long run to have a simple test code". Corollary of Golden Rule 3: you may hate this rule but unfortunately it is really true. Unfortunately I have not created a simple deforming grid PDE solver code. I think that the first step is for us to create such a code. I think the easiest way to do this is to merge deform.C and move2.C so that we solve an advection diffusion equation with twilight-zone on a deforming grid. Perhaps you want to make a first attempt at doing this? Otherwise I can try to put something together but I'm not sure when I can get to it. ...Bill