[petsc-users] TS and snes_grid_sequence

Hong Zhang hongzhang at anl.gov
Wed Feb 10 17:23:39 CST 2016

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.

> On Feb 10, 2016, at 4:45 PM, Jed Brown <jed at jedbrown.org> wrote:
> Hong Zhang <hongzhang at anl.gov> 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).

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