[petsc-users] Questions about TS

[Jed Brown]

On Wed, Oct 19, 2011 at 16:08, Blaise Bourdin <bourdin at lsu.edu> wrote:

> I get it now... My confusion was due to being used to derived all scheme on
> the pde, then discretizing, whereas the documentation assumes that the
> equation is already discretized. I should have figured it out.
>

For software purposes and sometimes also for analysis, the "method of lines"
approach is often useful. That's how the TS interfaces are set up.


>
> Is it right to think of the division between ODE, DAE and IMEX in the
> documentation as Fully Explicit vs. Fully implicit vs. Semi-implicit?
>

Sure, but it's a matter of the interface more than the method. You can write

Xdot = F(X)

and use -ts_type beuler to solve it fully implicitly. I would consider

G(X,Xdot) = F(X)

to be the most general interface. When an IMEX method is used, this has the
clear semantics that G is implicit and F is explicit. Explicit methods
usually assume G(X,Xdot) = Xdot which is the default if you never call
TSSetIFunction. I think we will eventually have support for using standard
explicit methods where you just put the mass matrix into G, but that isn't
done yet.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111019/b5dd865a/attachment.htm>