#include <cstdio>
#include "mpi.h"
#include <iostream>

using namespace std;

float integral(const float a, const int n, const float h)
{
    float result = 0.0;
    const float local_h = h / 2.0;
    for (auto i = 0; i < n; i++)
    {
        const auto aij = a + i * h;
        result += (aij + local_h) * (aij + local_h) * h;
    }
    return result;
}

void main(int argc, char* argv[])
{
    int p,id;
    MPI_Status status;
    float result;

    const float a = 1;
    const float b = 4;
    const auto n = 100000;

    const auto dest = 0;
    const auto tag = 0;


    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &id);
    MPI_Comm_size(MPI_COMM_WORLD, &p);

    const auto h = (b - a) / n;
    const auto num = n / p;
    const auto range = (b - a) / p;
    const auto x = a + id * range;
    result = integral(x, num, h);

    printf("Rank %d, sum = %f\n", id, result);

    if (id == 0)
    {
        auto loacl_result = result;
        for (auto i = 1; i < p; i++)
        {
            const auto source = i;
            MPI_Recv(&result, 1, MPI_REAL, source, tag,
                     MPI_COMM_WORLD, &status);
            loacl_result += result;
        }
        printf("Total sum = %f\n", loacl_result);
    }
    else
        MPI_Send(&result, 1, MPI_REAL, dest, tag,
                 MPI_COMM_WORLD);

    MPI_Finalize();
}