On Sat, May 9, 2020 at 10:10 AM hritikesh semwal via discuss < [email protected]> wrote:

Hello,

I have following two questions with MPI,

1. Do I need to give a separate input file to each processor in a group or all of them can read the input from a single file? All data inside the file should be read by every processor.

You can read the input file from every process but it isn't a good idea. Read the input file from rank 0 and broadcast the contents. This assumes that your input file is small. If your input file is huge, then you should consider designing it for parallel reading with MPI_File_* functions.

2. Can you please tell me what is the difference between MPI_Neighbor_alltoallw and MPI_Ineighbor_alltoallw? As I read in MPI 3.0 document that MPI_Neighbor_alltoallw also used non-blocking send and receive inside its execution.

MPI_Neighbor_alltoallw is a blocking function while MPI_Ineighbor_alltoallw is not. Using non-blocking send and receive inside its execution does not mean that MPI_Neighbor_alltoallw doesn't block - if that is how it's implemented, then there will be the equivalent of a MPI_Waitall before the function returns. But in any case, just because the MPI document suggests a possible implementation does not mean that is how all implementations work. Jeff

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-- Jeff Hammond [email protected] http://jeffhammond.github.io/