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

void Get_data(int p, int my_rank, double* a_p, double* b_p, int* n_p);

double Trap(double local_a, double local_b, int local_n,
           double h);  

double f(double x); 


int main(int argc, char* argv[]) {
    int         my_rank;   
    int         p;         
    double      a;        
    double      b;        
    int         n;        
    double      h;        
    double      local_a;   
    double      local_b;   
    int         local_n;  
                           
    double      my_area;  
    double      total;         
    int         source;    
    int         dest = 0; 
    int         tag = 0;
    MPI_Status  status;

   
    MPI_Init(&argc, &argv);

    
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

   
    MPI_Comm_size(MPI_COMM_WORLD, &p);

    Get_data(p, my_rank, &a, &b, &n);

    h = (b-a)/n;    
    local_n = n/p;  

   
    local_a = a + my_rank*local_n*h;
    local_b = local_a + local_n*h;
    my_area = Trap(local_a, local_b, local_n, h);

    
    if (my_rank == 0) {
        total = my_area;
        for (source = 1; source < p; source++) {
            MPI_Recv(&my_area, 1, MPI_DOUBLE, source, tag,
                MPI_COMM_WORLD, &status);
            total = total + my_area;
        }
    } else {  
        MPI_Send(&my_area, 1, MPI_DOUBLE, dest,
            tag, MPI_COMM_WORLD);
    }

    
    if (my_rank == 0) {
        printf("With n = %d trapezoids, our estimate\n",
            n);
        printf("of the area from %f to %f = %.15f\n ",
            a, b, total);
    }

    
    MPI_Finalize();

    return 0;
} 
void Get_data(int p, int my_rank, double* a_p, double* b_p, int* n_p) {
   int        q;
   MPI_Status status;

   if (my_rank == 0) {
      printf("Enter a, b, and n\n");
      scanf("%lf %lf %d", a_p, b_p, n_p);

      for (q = 1; q < p; q++) {
         MPI_Send(a_p, 1, MPI_DOUBLE, q, 0, MPI_COMM_WORLD);
         MPI_Send(b_p, 1, MPI_DOUBLE, q, 0, MPI_COMM_WORLD);
         MPI_Send(n_p, 1, MPI_INT, q, 0, MPI_COMM_WORLD);
      }
   } else {
      MPI_Recv(a_p, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, &status);
      MPI_Recv(b_p, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, &status);
      MPI_Recv(n_p, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
   }
}  
 
double Trap(
          double  local_a   ,double  local_b   ,int     local_n   ,double  h         ) {
    double my_area;  
    double x;
    int i;

    my_area = (f(local_a) + f(local_b))/2.0;
    x = local_a;
    for (i = 1; i <= local_n-1; i++) {
        x = local_a + i*h;
        my_area = my_area + f(x);
    }
    my_area = my_area*h;

    return my_area;
} 
double f(double x) {
    double return_val;

    return_val = sin(x);

    return return_val;
}