[petsc-users] RK substeps

[Jed Brown]

On Fri, Nov 11, 2011 at 08:29, Juha Jäykkä <juhaj at iki.fi> wrote:

> Right. I just may need them for my boundary conditions: they depend on time
> derivatives, i.e. change in value of something between time steps. It may
> be
> necessary to compute those values separately for each substep, but I am not
> sure yet. I am just making sure I have easy access to them - from your
> answer
> it looks like I need to hard code them.
>

We pass in the time of the stage when your RHSFunction is called. If you
haven't eliminated boundary conditions, your system is likely
differential-algebraic, in which case you can use the IFunction interface
with an implicit or IMEX method (e.g. TSARKIMEX, TSROSW). This has been
improved in petsc-dev, so consider using it if you want the latest
adaptivity and IMEX features.
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