You cannot change the sizes after the matrix is assembled, nor can you duplicate a matrix with a different layout from the original matrix.
If you want to partition a matrix that already exists use MatCreateSubMatrix(). You can use ISCreateStride() to generate the IS that define the new layout you want. Barry But when possible I would set the sizes of the matrix before loading it since then you don't need two copies of the matrix in memory at the same time. > On May 15, 2019, at 8:06 AM, Eda Oktay via petsc-users > <petsc-users@mcs.anl.gov> wrote: > > Dear Matt, > > I am trying to distribute the matrix after loading it. So I tried something > like this: > > Mat B; > PetscInt bm,bn; > MatSetSizes(B,kk,kk,PETSC_DETERMINE,PETSC_DETERMINE); > MatDuplicate(A,MAT_COPY_VALUES,&B); > MatGetLocalSize(B,&bm,&bn); > > where A is the original matrix (10*10) and kk is one the local sizes of A > (kk=4 so I want to divide A into 4*4 and 6*6). However, I get error in > MatSetSizes part and when I printed bm and bn, I get 5. In other words, B is > divided equally even though I tried to divide it unequally. Am I using > MatSetSizes wrong? > > Thanks, > > Eda > > Matthew Knepley <knep...@gmail.com>, 15 May 2019 Çar, 14:51 tarihinde şunu > yazdı: > On Wed, May 15, 2019 at 7:35 AM Eda Oktay via petsc-users > <petsc-users@mcs.anl.gov> wrote: > Hello, > > I am trying to divide a matrix into unequal sized parts into different > processors (for example I want to divide 10*10 matrix into 4*4 and 6*6 > submatrix in two processors). When my program reads a matrix from file, it > automatically divides it into equal parts and then I can't change local sizes. > > How can I decompose a matrix that is read from a file? > > MatLoad() takes a matrix argument. I believe you can use MatSetSizes() before > loading to get the distribution you want. > > Matt > > Thanks, > > Eda > > > -- > 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/
