Hi Matthew, Supposed for my 8x8 grid, there's ghost cells on the edge, hence changing to 0->9 x 0->9 no. of grids. I divide them along the y direction such that for 4 processors,
myid=0 y=0 to 2 myid=1 y=3 to 4 myid=2 y=5 to 6 myid=3 y=7 to 9 therefore, for myid = 0 and 3, i'll have slightly more cells. however, for VecCreateMPI, if i use: call VecCreateMPI(MPI_COMM_WORLD,PETSC_DECIDE,size_x*size_y,b_rhs,ierr) should size_x = size_y = 8? Different myid also has different no. of cells. however the PETSC_DECIDE is the same for all processors. Will that cause error? Thank you very much and have a nice day! Yours sincerely, Wee-Beng Tay Matthew Knepley wrote: > On Mon, Apr 13, 2009 at 10:50 PM, Wee-Beng TAY <zonexo at gmail.com > <mailto:zonexo at gmail.com>> 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. > > Matt > > > > 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 lead. > -- Norbert Wiener
