On Mon, Jan 27, 2025 at 8:42 AM Pierre Jolivet <pie...@joliv.et> wrote:
> > On 27 Jan 2025, at 2:23 PM, medane.tchako...@univ-fcomte.fr wrote: > > > > Dear PETSc users, > > > > I hope this message finds you well. I don’t know If my question is > relevant, but I’am currently working with DENSE type matrix, and would like > to copy one matrix R_part [ n/2 x m] (resulted from a MatMatMult operation) > into another dense matrix R_full [n x m]. > > Both matrices being on the same communicator, I would like to > efficiently copy R_part in the first half of R_full. > > I have being using MatSetValues, but for large matrices, the subsequent > assembling operation is costly. > > Could you please share the output of -log_view as well as a single file > that will be generated with -info dump (e.g., dump.0, the file associated > to process #0)? > This shouldn’t be that costly, so there may be an option missing, like > MAT_NO_OFF_PROC_ENTRIES. > Anyway, if you want to optimize this, the fastest way would be to call > MatDenseGetArray[Read,Write]() and then do the necessary PetscArraycpy(). > The other alternative (which I think makes cleaner code) is to use https://urldefense.us/v3/__https://petsc.org/main/manualpages/Mat/MatDenseGetSubMatrix/__;!!G_uCfscf7eWS!ZOoOupB2xSO9fOY1fdeyPQU6bNVEuctFDItgqZzhKerRBnX3177w7U4_2rlep0tcSVOrNgKt75z9xd8BvjI9$ to create your R_part matrix. Then you are directly acting on the memory you want when assemble the smaller matrix. THanks, Matt > Thanks, > Pierre > > > Please could you suggest me some strategies or functions to do this > efficiently. > > > > Thank you for your time and assistance. > > > > Best regards, > > Tchakorom Medane > > > > -- 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://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!ZOoOupB2xSO9fOY1fdeyPQU6bNVEuctFDItgqZzhKerRBnX3177w7U4_2rlep0tcSVOrNgKt75z9xRlvvjmx$ <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!ZOoOupB2xSO9fOY1fdeyPQU6bNVEuctFDItgqZzhKerRBnX3177w7U4_2rlep0tcSVOrNgKt75z9xasPQhF0$ >
