75 lines
1.5 KiB
C
75 lines
1.5 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <mpi.h>
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int main(int argc, char *argv[])
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{
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int value;
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int my_rank, size;
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int previous, next;
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MPI_Status status;
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MPI_Init(NULL, NULL);
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// Get number of processes
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MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
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MPI_Comm_size(MPI_COMM_WORLD, &size);
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// determine my neighbours according to my rank
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if (my_rank == 0)
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{
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previous = size - 1;
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next = my_rank + 1;
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}
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else if (my_rank == size - 1)
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{
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previous = my_rank - 1;
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next = 0;
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}
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else
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{
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previous = my_rank - 1;
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next = my_rank + 1;
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}
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value = 1;
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// The nodes, starting with node 0, transmit the value to each other,
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// each time multiplying it by 2.
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// At the end of the transmission, node 0 receives the value 2^(size-1)
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//
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// Instruction: before each send and after each receive, each node displays
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// - its rank
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// - the type communication (send, recv)
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// - the value
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// receive value from previous node
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if (my_rank != 0)
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{
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MPI_Recv(&value, 1, MPI_INT, previous, 0, MPI_COMM_WORLD, &status);
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printf("RECEIVED from process %d of %d, value = %d\n", my_rank, size, value);
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value = value * 2;
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}
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else
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{
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printf("START, value = %d\n", value);
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}
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printf("SENDING from process %d of %d, value = %d\n", my_rank, size, value);
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// send value to next node
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if (my_rank != size - 1)
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{
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MPI_Send(&value, 1, MPI_INT, next, 0, MPI_COMM_WORLD);
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}
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else
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{
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printf("The End, value = %d\n", value);
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}
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MPI_Finalize();
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return EXIT_SUCCESS;
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}
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