I don't understand. Why do you wish the new matrix-matrix product vector to have the same nonzero pattern as the basic dm matrix?
If you multiple two dm matrices together it will generally have a larger stencil then the dm matrix but this is normal and the new product matrix handles it correctly. You should not copy this new "larger" matrix into a dm matrix. When you do MatAXPY() or MatAYPX() you should put the result into the product matrix, not the dm matrix and you can use SUBSET_NONZERO_PATTERN to make it reasonably efficient. Barry > On Aug 12, 2021, at 10:31 AM, Matthew Knepley <knep...@gmail.com> wrote: > > On Thu, Aug 12, 2021 at 10:44 AM Alfredo J Duarte Gomez <aduar...@utexas.edu > <mailto:aduar...@utexas.edu>> wrote: > Good morning, > > I am currently having some trouble in the creation of some matrices. > > I am using structured dmda objects to create matrices using the DMCreate() > function. > > One of these matrices will be the result of a matrix-matrix product of two of > these dm matrices. > > I know that the matrix product will have more nonzero entries or at least a > bigger stencil than the original dm matrices, however I accounted for that > when I set the DMDA stencil width in the initial creation. > > By default, we put zeros into those locations, so you would expand that > stencil when doing MatMatMult(). You can use > > -dm_preallocate_only > > to prevent the zeros from being included. However, then your target matrix > would not have those locations, so you would > need to turn that off before creating the product matrix, or you could just > make two DMDA with different stencils, since they > are really small. This later solutions sounds cleaner to me. > > Thanks, > > Matt > > The problem is that even with that, the resulting matrix-matrix product has a > bigger stencil as evidenced by failure in subsequent matrix copy/addition > operations using SAME_NONZERO_PATTERN. > > Judging by the difference of the nonzero entries I believe that initial zero > entries (the ones I initialized to eventually hold this expaned stencil) on > the original dm matrices are being combined to further expand the stencil of > the product matrix. > > Is there any way of getting a matrix-matrix product that will keep the same > nonzero pattern as the dm matrices? > > I have tried both MatMatMult() and the MatProductCreate() sequence so far, > but both produce nonzero patterns that do not match the dm nonzero pattern. > > Thank you, > > -Alfredo > > > > -- > Alfredo Duarte > Graduate Research Assistant > The University of Texas at Austin > > > -- > 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/>
