I am having a problem, and every solution I can think of would seem to do violence to encapsulation or to DMKSP/DMSNES. I want to have GMG automatically work on the velocity part of Stokes. So I give -fieldsplit_velocity_pc_type mg in SNES ex62. This complains that the KSP has a DM but KSPSetComputeOperator() has not been called. It is fine on the global system because SNES called that in SNESSetupMatrices(). Thus in FieldSplit, I inserted { PetscErrorCode (*func)(KSP,Mat,Mat,void*); void *ctx; ierr = DMKSPGetComputeOperators(pc->dm, &func, &ctx);CHKERRQ(ierr); ierr = DMKSPSetComputeOperators(dms[i], func, ctx);CHKERRQ(ierr); } where we call KSPSetDM(). However, this does not work, because the subDM has a new DMSNES, which does not have the information about the problem. Solution #1: Copy the info from the old DMSNES to the subDMSNES. This inserts a dependence between KSP and SNES which we do not want. Solution #2: Have DMCreateSubDM() copy everything from the solvers. This also inserts dependencies, unless we have a "copy everything" mechanism, but is this what we want. Solution #3: Rethink DMKSP/DMSNES. Is this how we should store problem information. Dave already had another problem with the organization. What should be done? I have never understood this construct very well. Right now, this is holding up doing some computations I need. Thanks, Matt -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>