/* 
Jonathan Hauenstein - University of Notre Dame
Center for Applied Mathematics Minicourse on Parallel Computing
April 24, May 1, May 8, 2008
Sample programs are designed for educational use 
*/

#include "trapezoid.h"
#include <mpi.h>

void create_trapInfo(MPI_Datatype *mpi_trapInfo)
{ // create the MPI datatype mpi_trapInfo
  MPI_Aint sAdd, add; trapInfo A;

  // arrays for length, displacement and datatypes
  int blockLen[3] = {1,1,1}; // 1 element in each block
  MPI_Datatype types[3] = {MPI_INT, MPI_DOUBLE, MPI_DOUBLE};
  MPI_Aint indices[3] = {0,0,0};

  // calculate the starting address
  MPI_Address(&A.n, &sAdd);
  // calculate the second address and compute the displacement
  MPI_Address(&A.a, &add); indices[1] = add - sAdd;
  // calculate the third address and compute the displacement
  MPI_Address(&A.b, &add); indices[2] = add - sAdd;

  // build the mpi datatype
  MPI_Type_struct(3, blockLen, indices, types, mpi_trapInfo);
  // commit the mpi datatype
  MPI_Type_commit(mpi_trapInfo);

  return;
}

void setup_my_info(trapInfo *my_info, double a, double b, int totalTrap, int my_id, int num_proc)
{ // setup my_info - if my_id == 0, distribute, otherwise, wait to recv
  MPI_Datatype mpi_trapInfo; MPI_Status status;
  // setup mpi_trapInfo
  create_trapInfo(&mpi_trapInfo);

  if (my_id == 0)
  { // split up the trapezoids equally between the other processes
    int i, trap_per_proc = totalTrap / num_proc;  double stepSize = 0; trapInfo send_info;
    // find the number of trapezoids left over that will be computed on id 0
    my_info->n = totalTrap - trap_per_proc * (num_proc - 1);

    // find the step size and setup the rest of my_info for id 0
    stepSize = (b - a) / totalTrap; 
    my_info->a = a; my_info->b = a + my_info->n * stepSize;

    // initialize send_info for the loop
    send_info.n = trap_per_proc; send_info.a = my_info->a; send_info.b = my_info->b;
    // send information out to the other processes
    for (i = 1; i < num_proc; i++)
    { // setup send_info
      send_info.a = send_info.b;  send_info.b = send_info.a + send_info.n * stepSize;
      // send it
      MPI_Send(&send_info, 1, mpi_trapInfo, i, 0, MPI_COMM_WORLD); 
    }
  }
  else
  { // recv my_info
    MPI_Recv(my_info, 1, mpi_trapInfo, 0, 0, MPI_COMM_WORLD, &status);
  }

  // clear mpi_trapInfo
  MPI_Type_free(&mpi_trapInfo);

  return;
}