[petsc-users] TS and snes_grid_sequence

[Hong Zhang]

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 <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).