On Tue, Feb 28, 2012 at 13:52, Dmitry Karpeev <karpeev@mcs.anl.gov> wrote:

I don't understand the need for multiple function evaluation routines and their explicit naming.

I think the situation here is completely analogous to the situation with matrices: I thought we agreed that each DM would be capable of generating a single matrix, the "Jacobian", rather than multiple matrices like J and J_pre, and that the different necessary matrices (again, e.g., J and J_pre) would instead be produced by their respective DMs -- the KSP DM and the PC DM, so to speak.  These subDMs would be pulled out of the SNES DM and passed to the corresponding KSP and PC objects.  Thus, a DM encapsulates a single "problem", and if we want to get a different problem -- the "exact" linearization of the original, for example -- we extract the KSP DM;  likewise, PC DM is an approximate linearization, and so on.

I don't think TS is any different -- we can have the TSI DM (maybe under a better name), which could have DMFormFunction encapsulating the IFunction (and, incidentally, a linearization encapsulating the mass matrix), etc.

I'm concerned that this becomes insanity. A single TS might need RHSFunction, IFunction, and IJacobian. They might also partition terms differently for the functions and the Jacobian. Having different DMs seems awfully confusing.

In short -- I'm for each DM having one function (DMFormFunction or, better, DMFormResidual) and one matrix (DMFormJacobian) -- *a* linearization of the residual.  All other functions and matrices are obtained from the corresponding subDMs.

The interface is actually different for these (compare TSIFunction, a transient residual, to SNESFunction)