HP-MPI User's Guide (11th Edition)

Example applications

multi_par.f

Appendix A252

partitioning used for the parallelization of the first outer-loop can

accommodate the other of the second outer-loop. The partitioning of the

array is shown in Figure A-1.

Figure A-1 Array partitioning

In this sample program, the rank n process is assigned to the partition n

at distribution initialization. Because these partitions are not

contiguous-memory regions, MPI's derived datatype is used to define the

partition layout to the MPI system.

Each process starts with computing summations in row-wise fashion. For

example, the rank 2 process starts with the block that is on the

0th-row block and 2nd-column block (denoted as [0,2]).

The block computed in the second step is [1,3]. Computing the first row

elements in this block requires the last row elements in the [0,3] block

(computed in the first step in the rank 3 process). Thus, the rank 2

process receives the data from the rank 3 process at the beginning of the

second step. Note that the rank 2 process also sends the last row

elements of the [0,2] block to the rank 1 process that computes [1,2] in

the second step. By repeating these steps, all processes finish

summations in row-wise fashion (the first outer-loop in the illustrated

program).

column block

row block