> On Jan 8, 2024, at 4:31 AM, Deuse, Mathieu via petsc-users > <petsc-users@mcs.anl.gov> wrote: > > Hello, > > I have a piece of code which generates a matrix in CSR format, but the > without sorting the column indexes in increasing order within each row. This > seems not to be 100% compatible with the MATMPIAIJ format: the documentation > of MatCreateMPIAIJWithArrays indeed mentions 'row-major ordering'. > > For example, consider the 2x2 matrix (1 2; 3 4), which in my code could be > stored as i=[0, 2, 4], j=[1, 0, 0, 1], v=[2, 1, 3, 4]. I can generate the > matrix as follows (on 1 proc): MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, 2, > 2, 2, 2, i, j, v, &matrix). This appears to work fine, and I can then use the > matrix in a KSP for example. However, if I try to update the entry values > (same order and values v=[2, 1, 3, 4]) with MatUpdateMPIAIJWithArray(matrix, > v), it seems that PETSc does not memorize the order of the column indexes and > the matrix that I get now is (2 1; 3 4). I get the same result with > MatUpdateMPIAIJWithArrays(matrix, 2, 2, 2, 2, i, j, v). On the other hand, if > the column indexes are sorted within each row (i=[0, 2, 4], j=[0, 1, 0, 1], > v=[1, 2, 3, 4]), then it works fine. I have attached a minimal working > example (C++). > > Can I safely rely on MatCreateMPIAIJWithArrays working fine with unsorted > column indexes as long as I do not use MatUpdateMPIAIJWithArray(s)?
Yes, this is correct. The column indices do not need to be sorted if you never call MatUpdateMPIAIJWithArray(). > Or should I do the sorting myself before calling MatCreateMPIAIJWithArrays? > (or alternatively use another matrix format). > > Thanks in advance for the help. > > Kind regards, > > Mathieu Deuse > <main.cpp>
