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Foil 49 Examples of MPI_ALLTOALL

From MPI Message Passing Interface Computational Science for Simulations -- Fall Semester 1998. by Geoffrey C. Fox, Nancy McCracken
1 All to All Communication with i'th location in j'th processor being sent to j'th location in i'th processor
2 Processor 0 1 2 3
3 Start (a0,a1,a2,a3) (b0,b1,b2,b3) (c0,c1,c2,c3) (d0,d1,d2,d3)
4 After (a0,b0,c0,d0) (a1,b1,c1,d1) (a2,b2,c2,d2) (a3,b3,c3,d3)
5 There are extensions MPI_ALLTOALLV to handle case where data stored in noncontiguous fashion in each processor and when each processor sends different amounts of data to other processors
6 Many MPI routines have such "vector" extensions
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