time steps in transient diffusion problem

Jeff

Look in the FORTRAN examples at the end of the Solver Modeling manual. There's some handy user Fortran for an adaptive time stepping scheme. If your coefficient loops are few (say less than three) you can set a multiplier to increase the time step size. If it's not converging in say 8 or 9 coefficient loops, it will reduce the time step.

I've modified it a bit to limit by a maximum time step, and not to increase until at least 10 steps in a row have met the minimum coefficient loops target (for stability) and it works pretty good. My problems have convection as well, but your diffusion problem aught to be able to work its way up to some large time steps as the gradients are reduced.

Jeff