# How to partition cartesian grid for MPI in fortran

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 January 16, 2008, 02:11 How to partition cartesian grid for MPI in fortran #1 CF Guest   Posts: n/a Hi, I'm programming in fortran and I'm trying to use a parallel solver known as Hypre, which is a library written in C. I'm working with cartesian grid and I wonder how I should partition my grid to run in parallel. Which is the best option for a cartesian grid of size_x*size_y, asuming to be divided to 4 grids? : 1. 4 (size_x/4)*size_y grids 2. 4 size_x*(size_y/4) grids 3. 4 (size_x/2)*(size_y/2) grids Is there some clear advantage of 1 over the other? Thanks

 January 17, 2008, 03:56 Re: How to partition cartesian grid for MPI in for #3 CF Guest   Posts: n/a Thank you Ananda for the detailed explanation. My domain is usually where nx>ny and hence I believe partition 1 is the best.

 January 17, 2008, 05:38 Re: How to partition cartesian grid for MPI in for #4 Ananda Himansu Guest   Posts: n/a You are welcome. I forgot to mention that satisfying criterion (d) should generally also allow you to minimize the number of stages of communication needed. In your particular case, all three partitions satisfy the criterion. For example, for partition 1, with contiguous subdomains numbered 1 through 4, the first stage of communication may involve subdomains 1 and 2 talking with each other, at the same time as subs 3 and 4 talk with each other. In the second (and last) stage, subs 1 and 4 talk with each other simultaneously with subs 2 and 3 talking with each other. For more complex partitions in 3-D, with more than two subdomain neighbors, you may use a graph-coloring algorithm to minimize the number of needed non-interfering communication stages.

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