The error messages provided by Francesco indicate a theta method is used in his code. So presumably he may happen to be using the default option of the theta method which is not good for stiff problems.
I mentioned the one-stage method just in response to the two ways Barry proposed. It might be easer to do the implementation based on beuler than methods with multi stages. Hong > On Feb 10, 2016, at 4:45 PM, Jed Brown <[email protected]> wrote: > > Hong Zhang <[email protected]> writes: > >> There is one particular integration method that may make the life easier — >> backward Euler. It has only one stage at each time step. >> >> To Francesco: which TS method are you using? Is it backward Euler or >> the default theta method? > > Default is forward Euler, which should almost never be used. > > Stages per step shouldn't be a serious concern. But -snes_grid_sequence > will never work for TS (it's a weird option that refines the SNES during > the solve -- it doesn't make semantic sense for TS).
