#include <math.h>
#include <mpi.h>
#include <stdio.h>


const double A1 = 0;
const double B1 = 100;
const double A2 = 0;
const double B2 = 100;
const double PI = 3.1415926;
const int N = 5e3;
const int M = 5e3;

#define PRECISION "3"


double f(double x, double y)
{
    return (exp(sin(PI * x) * cos(PI * y)) + 1) / ((B1 - A1) * (B2 - A2));
}


double q(int i, int j)
{
    double result = 1;
    if (i == 0 || i == N - 1)
    {
        result *= 0.5;
    }
    if (j == 0 || j == M - 1)
    {
        result *= 0.5;
    }
    return result;
}


void usual()
{
    double start_time = MPI_Wtime();

    double answer = 0;

    double h1 = (B1 - A1) / N;
    double h2 = (B2 - A2) / M;
    int i;
    for (i = 0; i < N; i++)
    {
        double xi = A1 + i * h1;
        int j;
        for (j = 0; j < M; j++)
        {
            double yi = A2 + j * h2;
            answer += f(xi, yi) * q(i, j);
        }
    }

    answer *= h1 * h2;

    printf("[%." PRECISION "lf sec] usual "
           "(answer = %." PRECISION "lf)\n",
               MPI_Wtime() - start_time, answer);
}


void external(int rank, int ncount)
{
    double start_time = MPI_Wtime();

    double answer = 0;

    double h1 = (B1 - A1) / N;
    double h2 = (B2 - A2) / M;
    int i;

    for (i = 0; i < N; i++)
    {
        if (rank == i % ncount)
        {
            double xi = A1 + i * h1;
            int j;
            for (j = 0; j < M; j++)
            {
                double yi = A2 + j * h2;
                answer += f(xi, yi) * q(i, j);
            }
        }
    }

    if (rank)
        MPI_Send(&answer, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
    else
    {
        for (i = 1; i < ncount; i++)
        {
            double s;
            MPI_Status st;
            MPI_Recv(&s, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, &st);
            answer += s;
        }

        answer *= h1 * h2;

        printf("[%." PRECISION "lf sec] parallel "
           "(answer = %." PRECISION "lf)\n",
               MPI_Wtime() - start_time, answer);
    }
}


int main()
{
    MPI_Init(NULL, NULL);

    int rank, ncount;
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &ncount);

    if (!rank)
    {
        printf("2.130997\n");
        usual();
    }
    external(rank, ncount);

    MPI_Finalize();
}