The questions arises because I want to use the solution of one PDE as initial condition to solve another. Then using NDSolve, the first solution is given by InterpolatingFunction. I tried, it takes the whole afternoon, almost kills my computer but still not giving any result. Another computer simply refused to work after sometime, telling me memory is not enough. My question is: 1. Can InterpolatingFunction be used as an initial condition in NDSolve? 2. Is there any way to bypass InterpolatingFunction? For example, make a list of values out of InterpolatingFunction, and then solve PDE based on this list of initial conditions, just like Plot and ListPlot?