> On 28. aug. 2014 20:52, Barry Smith wrote: > > > > On Aug 28, 2014, at 4:34 AM, Åsmund Ervik <[email protected]> wrote: > > > >> Hello, > >> > >> I am solving a pressure Poisson equation with KSP, where the initial > >> guess, RHS and matrix are computed by functions that I've hooked into > >> KSPSetComputeXXX. (I'm also using DMDA for my domain decomposition.) > >> > >> For (single-phase|two-phase) I would like to (reuse|not reuse) the > >> preconditioner. How do I specify that when using this way of setting the > >> operator? Is it toggled by whether or not I call KSPSetOperators before > >> each KSPSolve? (The manual does not mention KSPSetComputeXXX.) > > > > You should call KSPSetOperators() before each KSPSolve() (otherwise the > > function you provide to compute the matrix won’t be triggered). > > > > With PETSc 3.5 after the call to KSPSetOperators() call > > KSPSetReusePreconditioner() to tell KSP wether to reuse the preconditioner > > or build a new one. > > With PETSc 3.4 and earlier, the final argument to KSPSetOperators() > > would be MAT_SAME_PRECONDITIONER to reuse the preconditioner or > > MAT_SAME_NONZERO_PATTERN to construct a new preconditioner > >
Thanks Barry for the clarification. Is there an example somewhere that does this? All the ones I can find which use KSPSetComputeOperators() have no calls to KSPSetOperators(). I guess this is because they are only doing one linear solve? Furthermore, what should I pass in for Amat and Pmat to the KSPSetOperators() call? PetscNullObject, or do I get the Amat from the KSP somehow? Åsmund
