On Fri, Mar 1, 2024 at 11:10 AM Fabian Wermelinger <fab4...@posteo.ch> wrote:
> On Fri, 01 Mar 2024 10:09:17 -0600, Junchao Zhang wrote: > >No. MatMPIBAIJSetPreallocationCSR() copies the data, but > >VecCreateMPIWithArray() does not copy (only use pointers user provided). > > OK, my understanding was that MatMPIBAIJSetPreallocationCSR DOES NOT copy > since > it has direct access to matrix entries in the required PETSc layout -> > thank you > > >I think your intention is to avoid memory copies. > > Yes. (not only copies but also avoid unnecessary increase of memory > footprint) > > >If it is MATMPIAIJ, we can do > > MatMPIAIJSetPreallocationCSR(A, i, j, v); // let petsc copy i, j v > > > > // To quickly update A when you have an updated v[] > > > > MatUpdateMPIAIJWithArray(A, v); // copy v[], but faster than > MatSetValues() > > Thanks for this input! > > >But it seems we currently do not have a MatUpdateMPIBAIJWithArray() :( > > So when my v[] changed during iterations (only the v[] used during the > MatMPIBAIJSetPreallocationCSR call, the matrix structure/connectivity has > NOT > changed), it is not sufficient to just call KSPSetOperators() before > calling > KSPSolve()? Correct, your v[] is not shared with petsc > I must copy the updated values in v[] explicitly into the PETSc > matrix, then call KSPSetOperators() followed by KSPSolve()? (for every > iteration in my application) > Yes > > The preferred method then is to use MatSetValues() for the copies (or > possibly > MatSetValuesRow() or MatSetValuesBlocked())? > MatSetValuesRow() > > The term "Preallocation" is confusing to me. For example, > MatCreateMPIBAIJWithArrays clearly states in the doc that arrays are copied > (https://urldefense.us/v3/__https://petsc.org/release/manualpages/Mat/MatCreateMPIBAIJWithArrays/__;!!G_uCfscf7eWS!YLXb4luirYVduVkmxILIpET7hYcMAPTHUxHG7tR7os-mxUGGqYt_XTB0xPp5y5CU2gWNtgNEmD8gu3rmtqcqNfLfc2Oe$ > ), > I would > then assume PETSc maintains internal storage for it. If something is > preallocated, I would not make that assumption. > "Preallocation" in petsc means "tell petsc sizes of rows in a matrix", so that petsc can preallocate the memory before you do MatSetValues(). This is clearer in https://urldefense.us/v3/__https://petsc.org/release/manualpages/Mat/MatMPIAIJSetPreallocation/__;!!G_uCfscf7eWS!YLXb4luirYVduVkmxILIpET7hYcMAPTHUxHG7tR7os-mxUGGqYt_XTB0xPp5y5CU2gWNtgNEmD8gu3rmtqcqNdzTPnSf$ > Thank you for your time, I appreciate the inputs! > > All best, > > -- > fabs >
