[petsc-users] TS algo question

[Mark Adams]

Thanks, So I think I can move the IJacobian terms for the time dependant
equations to a matrix and apply this matrix in the RHSFunction, and use
backward Euler, which will mainly compute the auxiliary terms in the
solve.  But then the auxiliary variables will be a function of the state at
the end of the time step, whereas the forward Euler (or what the existing
code does) is computed with the state at the beginning of the time step.
This may not be the best way to verify this code ... Thanks again.

On Wed, May 27, 2015 at 9:41 PM, Jed Brown <jed at jedbrown.org> wrote:

> Mark Adams <mfadams at lbl.gov> writes:
>
> > I have setup the equations attached using TSSetIJacobian and
> >  TSSetIFunction.
> >
> > This is intended to be a fully implicit solvers with some auxiliary
> > variables.
> >
> > We want to verify the code with the current forward Euler solver.
>
> Mark, this is a DAE, so your "forward Euler" solver cannot literally be
> forward Euler.  It can be a semi-implicit method with differential
> variables propagated using forward Euler combined with solves at some
> point.  If you want flexibility in treating terms implicitly and
> explicitly, define both the RHSFunctian and IFunction.  Put those you
> want to treat implicitly in the IFunction.  (And make the IJacobian the
> Jacobian of the IFunction).
>
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