On Tue, Feb 3, 2009 at 9:25 AM, Yixun Liu <enjoywm at cs.wm.edu> wrote: > Hi, > I am confusing to the allocation for a parallel matrix in PETSC manual, > > "If PETSC DECIDE is not used for the arguments m and n, then the user > must ensure that they are chosen > to be compatible with the vectors. To do this, one first considers the > matrix-vector product y = Ax. The m > that is used in the matrix creation routine MatCreateMPIAIJ() must match > the local size used in the vector > creation routine VecCreateMPI() for y. Likewise, the n used must match > that used as the local size in > VecCreateMPI() for x." > > Since the process holds all the columns, why does it only hold part of > vector x? Is it convenient for the matrix vector multiplication?
I am not sure I understand your question. However, Mat objects do hold all columns of a row. The local column size 'n' is used to match against a Vec, not for storage. Matt > Thanks. > > Yixun -- 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
