On Fri, Feb 10, 2012 at 16:13, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
> Well, two is the number that's used in KSP and SNES. > DM can be used outside of KSP and SNES. It may well make sense to have J and Jpre corresponding to the implicit part of an equation plus a "mass matrix" to be used for "explicit stages" in an IMEX method. That is three (or even four if the mass matrix needs a preconditioner) extracted from the same DM (in different solves). > > With the current API SNES actually uses the same matrix for the Jacobian > and preconditioner, if the matrix is obtained from a DM, which is limiting. > It is natural to have a "geometric" backend (e.g., libMesh or MOOSE) > interact with the algebraic objects (PETSc's SNES, KSP) through the DM as > much as possible, since the DM (its impl, rather) carries all of the > necessary mesh and discretization information in one place. Yet, currently > this interaction is limited as compared to the "bare" SNES/KSP interface, > in part because of the one matrix limitation. > I agree that it's clumsy that -snes_mf_operator is the only "nice" way to get matrix-free in some cases, and it only gives you one kind of matrix-free. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20120210/ae810e80/attachment.html>
