[FLASH-USERS] split solver, timestepping/refinement and the time accuracy order

[Klaus Weide]

On Tue, 23 Apr 2013, Andrea Gatto wrote:

> for stability reasons I find myself forced to reduce the timestep after
> the first call (in the first half of the Strang splitting loop) of the
> source terms when using a split solver in Driver_evolveFlash.F90 .
> This means that the second call of the solver (in the second half of the
> loop) is performed on a different (smaller) timestep.

Hello Andrea,

I am wondering why you want to use the split solver?  It seems that
your questions would not even arise if you used the Unsplit variant of 
Driver_evolveFlash.F90 .

> Could this cause the Strang splitting scheme accuracy order to be reduced
> from 2 to 1? 

Yes, I think so.

> Are there any other problems with this timestep change?
> Could this problem happen also when I force a refinement in a certain
> region during the first call of the source terms?

I think changing the Grid in the middle of one "split timestep" (which 
should just be two steps of the same time interval) is asking for trouble;
again, why not go with the simpler Unsplit scheme?

Klaus