Use of MatCreateMPIAIJ and VecCreateMPI when ghost cells are present

Matthew Knepley knepley at
Tue Apr 14 06:21:38 CDT 2009

On Mon, Apr 13, 2009 at 10:50 PM, Wee-Beng TAY <zonexo at> wrote:

> Hi,
> In the past, I did not use ghost cells. Hence, for e.g., on a grid 8x8, I
> can divide into 8x2 each for 4 processors i.e. divide the y direction
> because in my computation, usually y no. of cells > x no. of cells. this
> will minimize the exchange of values.
> Now, with ghost cells, it has changed from x,y=1 to 8 to 0 to 9, i.e., the
> grid is now 10x10 hence to divide to 4 processors, it will not be an integer
> because 10/4 is not an interger. I'm thinking of using 6x6 grid, and
> including ghost cells becomes 8x8. Is this the right/best way?
> Thank you very much and have a nice day!

Usually it is not crucial to divide the grid into exactly equal parts since
the number of elements is large.


> Yours sincerely,
> Wee-Beng Tay
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
-- Norbert Wiener
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