Got it, thanks Matt! Matthew Knepley <[email protected]> 于2023年5月16日周二 17:28写道：
> On Tue, May 16, 2023 at 11:12 AM K. Wu <[email protected]> wrote: > >> Hi Matt, >> >> >> >> I am using two PETSc DM, one for vertices (nodes), and one for cells >> (elements). >> > > I assume you mean DMDA. > > >> I want to do the following operation: >> >> x is a global vector generated from DM vertices, with length Nn. y is a >> global vector generated from DM cells, with length Ne. I want to generate a >> sparse matrix A with size Ne x Nn, so that y = A*x. >> >> The entry of A is set to a constant value, e.g., 1/4, if the >> corresponding vertex belongs to the cell. >> > Yes, this is straightforward. First create the matrix with the same local > sizes as the vectors from the DMDAs. > Each row will have the same number of nonzeros (the number of vertices on > each cell), so preallocation is > easy. Finally, I would loop over the vertex grid, and put in weights for > (i, j, k) and +1 in each direction for cell (i, j, k). > > Thanks, > > Matt > > >> >> >> Hope I make it clear, thanks! >> >> >> >> Regards, >> >> Kai >> >> Matthew Knepley <[email protected]> 于2023年5月16日周二 16:29写道： >> >>> On Tue, May 16, 2023 at 10:27 AM K. Wu <[email protected]> wrote: >>> >>>> Hi all, >>>> >>>> Good day! >>>> >>>> I am currently working on interploating the nodal field vector I >>>> obtained to its corresponding elemental field vector. I am doing it in a >>>> simple way by using structured mesh, the element value is just the average >>>> of its corresponding nodal values. >>>> >>>> Is it possible to generate a connectivity matrix to implement this >>>> function? I also need this matrix later on to do a reverse transformation. >>>> >>>> I am wondering is there a way in PETSc to generate this connectivity >>>> matrix between nodal and elemental mesh. Or is there any better way to >>>> accomplish this? >>>> >>>> Thanks for your kind help! >>>> >>> >>> 1. Are you using a PETSc DM, or your own mesh? >>> >>> 2. In order to define what you mean, you have to attach function spaces >>> (or something equivalent) to the >>> two representations. Do you mean linear interpolation between >>> vertices and constants on cells? >>> >>> Thanks, >>> >>> Matt >>> >>> >>>> Best regards, >>>> Kai >>>> >>> >>> >>> -- >>> 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/> >>> >> > > -- > 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/> >
