[petsc-dev] SNES, Coloring, DM, and TS

[Jed Brown]

On Tue, Feb 28, 2012 at 14:20, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> Just out of curiosity: how many transient problems have we seen where the
> transient residual doesn't split like R(U,U_t) = R_0(U_t) + R_1(U)?  There
> is the issue of explicit dependence on time, but if that could be
> addressed, the problem would naturally split and, as a side benefit, there
> would be a natural "mass" matrix coming out of the linearization of R_0.
>

Moving mesh problems often have terms involving both U_t and U. The IMEX
interface is

g(t,X,X_t) = f(t,X)

which lets us split the implicit and explicit parts. Having a separate mass
matrix is normally quite wasteful and it's confusing for people doing
matrix-free methods where it is natural to keep both together.
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