scf_celebic/ex7/code/task3/main.cpp

#include <algorithm>
#include <iostream>
#include <mpi.h>
#include <vector>
using namespace std;


void DebugVector(const vector<double> &xin, MPI_Comm icomm) {
    int rank, size;
    MPI_Comm_rank(icomm, &rank);
    MPI_Comm_size(icomm, &size);

    int next_process = 0;
    while (next_process != -1) {
        // Print the local vector for each process
        if (rank==next_process){
            cout << "x_" << rank << " = ";
            for (const auto& value : xin) {
                cout << value << " ";
            }
            cout << endl;
        }
        MPI_Barrier(icomm);

        if (rank == 0) {
            cout << "Enter rank (0-" << size - 1 << ") or -1 to exit: ";
            cin >> next_process;
        }
        MPI_Bcast(&next_process, 1, MPI_INT, 0, icomm);
        MPI_Barrier(icomm);
    }
}



double par_scalar(const vector<double>& x, const vector<double>& y, MPI_Comm icomm) {
 
    double local_dot = 0.0;
    for (size_t i = 0; i < x.size(); ++i) {
        local_dot += x[i] * y[i];
    }

    double global_dot = 0.0;
    MPI_Allreduce(&local_dot, &global_dot, 1, MPI_DOUBLE, MPI_SUM, icomm);

    return global_dot;
}


tuple<double,double> find_global_minmax(const vector<double>& xin, MPI_Comm icomm) {
    int rank, size;
    MPI_Comm_rank(icomm, &rank);
    MPI_Comm_size(icomm, &size);
    // Find local min/max
    double local_min = *min_element(xin.begin(), xin.end());
    double local_max = *max_element(xin.begin(), xin.end());
    // Gather local mins/maxs in vector
    vector<double> local_min_vector(size);
    vector<double> local_max_vector(size);
    MPI_Gather(&local_min, 1, MPI_DOUBLE, local_min_vector.data(), 1, MPI_DOUBLE, 0, icomm);
    MPI_Gather(&local_max, 1, MPI_DOUBLE, local_max_vector.data(), 1, MPI_DOUBLE, 0, icomm);
    // Find global min/max
    double global_min(0);
    double global_max(0);
    if (rank==0) {
        global_min = *min_element(local_min_vector.begin(), local_min_vector.end());
        global_max = *max_element(local_max_vector.begin(), local_max_vector.end());
    }
    // Broadcast global min/max
    MPI_Bcast(&global_min, 1, MPI_DOUBLE, 0, icomm);
    MPI_Bcast(&global_max, 1, MPI_DOUBLE, 0, icomm);
    
    return make_tuple(global_min, global_max);
}


tuple<double,double> find_global_minmax_Allreduce(const vector<double>& xin, MPI_Comm icomm) {
    double local_min = *min_element(xin.begin(), xin.end());
    double local_max = *max_element(xin.begin(), xin.end());
    double global_min(0);
    double global_max(0);
    MPI_Allreduce(&local_min, &global_min, 1, MPI_DOUBLE, MPI_MIN, icomm);
    MPI_Allreduce(&local_max, &global_max, 1, MPI_DOUBLE, MPI_MAX, icomm);
    return make_tuple(global_min, global_max);
}


int main(int argc, char *argv[]) {
    MPI_Comm icomm = MPI_COMM_WORLD;
    MPI_Init(&argc, &argv);
    int rank, size;
    MPI_Comm_rank(icomm, &rank);
    MPI_Comm_size(icomm, &size);

    if (rank==0) {
        cout << "\n There are " << size << " processes running.\n";
    }

    // Create vectors
    size_t n=20;
    vector<double> local_vector(n);
    vector<double> local_vector_inv(n);
    for (size_t i=0; i<n; ++i) {
        // local_vector[i] = rank*n + i+1;                  
        // local_vector_inv[i] = 1.0/(local_vector[i]);

        local_vector[i] = rank*100.0 + (i%5)*10.0 + i;      // EX8
        local_vector_inv[i] = 1.0/(local_vector[i]+1.0);
    }

    
    MPI_Barrier(icomm);
    if (rank == 0) {printf("\n\n-------------- Task 5 --------------\n\n");}
    DebugVector(local_vector, icomm);


    MPI_Barrier(icomm);
    if (rank == 0) {printf("\n\n-------------- Task 6 --------------\n\n");}
    double result = par_scalar(local_vector, local_vector_inv, icomm);
    if (rank == 0) {printf("Global scalar product: %f\n", result);}


    MPI_Barrier(icomm);
    if (rank == 0) {printf("\n\n-------------- Task 7 --------------\n\n");}
    auto [min, max] = find_global_minmax(local_vector, icomm);
    if (rank == 0) {printf("Global min: %.0f | global max: %.0f\n\n", min, max);}
    
    MPI_Barrier(icomm);
    tuple(min, max) = find_global_minmax_Allreduce(local_vector, icomm);
    if (rank == 0) {printf("Global min: %.0f | global max: %.0f\n", min, max);}

    
    MPI_Barrier(icomm);
    if (rank == 0) {printf("\n\n-------------- Task 8 --------------\n\n");}

    if (rank == 0) {printf("\n---- MPI_Alltoall ----\n");}
    vector<double> recv(n);
    MPI_Alltoall(local_vector.data(), 5, MPI_DOUBLE, recv.data(), 5, MPI_DOUBLE, icomm);
    DebugVector(recv, icomm);
    
    MPI_Barrier(icomm);
    if (rank == 0) {printf("\n---- MPI_Alltoall using MPI_IN_PLACE ----\n");}
    MPI_Alltoall(MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, local_vector.data(), 5, MPI_DOUBLE, icomm);
    DebugVector(local_vector, icomm);

    
    MPI_Finalize();
    return 0;
}