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48 lines
1.9 KiB
C++
48 lines
1.9 KiB
C++
#include <mpi.h>
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#include <iostream>
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/*
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MPI_Reduce(
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void* send_data, //the element to apply the reduce
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void* recv_data, //the reduce result
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int count, //size of result in recv_data is sizeof(datatype)*count
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MPI_Datatype datatype, //type of element
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MPI_Op op, //operation to apply. Can also be defined custom operation
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int root, //rank of the process that receive result
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MPI_Comm comm //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(&argc, &argv); //Initialize the MPI environment //TODO perche qui non (NULL, NULL) ??
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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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float rand_nums[4] = {1,2,3,42};
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int size = 4; //Related to the correct dize of rand_nums array
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float local_sum = 0;
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for(int i=0; i<size; i++) //each process compute the sum locally
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local_sum += rand_nums[i];
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std::cout << "Process (rank " << world_rank+1 << "/" << world_size << ") sum is " << local_sum << " avg is " << local_sum/size << std::endl;
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if(world_rank%2 == 0) //explicative example part
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local_sum = 1;
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float global_sum;
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//MPI_Reduce(send_data, recv_data, count, datatype, op, root, comm)
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MPI_Reduce(&local_sum, &global_sum, 1, MPI_FLOAT, MPI_SUM, 2, MPI_COMM_WORLD);
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/*Il processo root(suppongo), esegue l'operazione specificata su ogni elemento send_data che gli altri processi hanno riempito*/
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if(world_rank == 2)
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std::cout << " USING REDUCE:" << std::endl << "Process (rank " << world_rank+1 << "/" << world_size << ") sum is " << global_sum << " avg of averages is " << global_sum/(world_size*size) << std::endl;
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MPI_Finalize(); //Clean up the MPI environment
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return 0;
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} |