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42 lines
1.8 KiB
C++
42 lines
1.8 KiB
C++
#include <mpi.h>
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#include <iostream>
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/*
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Creates new communicators by "splitting" a communicator into a group of sub-communicators based on the input values color and key.
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MPI_Comm_split(
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MPI_Comm comm, //communicator to split
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int color, //determines to which new communicator each process will belong. Same color same communicator
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int key, //determ the order(rank) within each new communicator. The smallest key value is assigned to 0, next to 1 and so on
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MPI_Comm* newcomm //new communicator
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)
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*/
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int main(int argc, char* argv[])
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{
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MPI_Init(NULL, NULL); //Initialize the MPI environment
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int world_size;
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MPI_Comm_size(MPI_COMM_WORLD, &world_size); //Get the number of processes
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int world_rank;
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MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); //Get the number of process
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//In the following code we suppose to have 10 processes and we want to split them in sub groups "rows" as they are a 2x5 Matrix
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int color = world_rank / 2; //Determine color based on row
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MPI_Comm row_comm; //To free
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//MPI_Comm_split(comm, color, key, newcomm)
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MPI_Comm_split(MPI_COMM_WORLD, color, -world_rank, &row_comm);
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int row_size;
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MPI_Comm_size(row_comm, &row_size); //Get the number of processes related to the communicator
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int row_rank;
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MPI_Comm_rank(row_comm, &row_rank); //Get the number of process related to the communicator
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std::cout << "Process (rank " << world_rank+1 << "/" << world_size << ") is splitted to sub-group " << row_rank+1 << "/" << row_size << "-" << color << " (row/size-color)" << std::endl;
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MPI_Comm_free(&row_comm); //We have to free the communicator that we created above
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MPI_Finalize(); //Clean up the MPI environment
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return 0;
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} |