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57 lines
2.4 KiB
C++
57 lines
2.4 KiB
C++
#include <mpi.h>
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#include <cmath>
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#include <iostream>
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/*
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MPI_Allreduce(
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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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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[10] = {1,2,3,42,55,66,71,82,93,190};
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int size = 10; //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 << "STEP1-Process (rank " << world_rank+1 << "/" << world_size << ") sum is " << local_sum << std::endl;
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//Reduce all the local sums into the global sum in order to calculate the mean
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float global_sum;
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//MPI_Allreduce(send_data, recv_data, count, datatype, op, comm)
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MPI_Allreduce(&local_sum, &global_sum, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);
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/*Come la Reduce ma senza il processo root perche' il risultato viene distribuito a tutti i processi*/
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float mean = global_sum/(size * world_size);
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float local_sq_diff = 0;
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for(int i=0; i<size; i++) //each process compute the sum of the squared differences from the mean (locally)
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local_sq_diff += (rand_nums[i] - mean) * (rand_nums[i] - mean);
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std::cout << "STEP2-Process (rank " << world_rank+1 << "/" << world_size << ") sum of the squared differences from the mean is " << local_sq_diff << std::endl;
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float global_sq_diff;
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MPI_Reduce(&local_sq_diff, &global_sq_diff, 1, MPI_FLOAT, MPI_SUM, 1, MPI_COMM_WORLD);
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if(world_rank == 1)
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std::cout << " FINAL RESULT:" << std::endl << "Process (rank " << world_rank+1 << "/" << world_size << ") mean is " << mean << ", standard deviation is " << sqrt(global_sq_diff/(size*world_size)) << std::endl;
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MPI_Finalize(); //Clean up the MPI environment
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return 0;
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} |