2016-04-18-4.c

#include <mpi.h>
#include <stdio.h>
#define W MPI_COMM_WORLD
#define n 99999

void printArray(int size, double array[size], int rank) {
  for (int i = 0; i < size; i++) {
    if (rank == -1) printf("%4.4f ", array[i]);
    else printf("{%d}%4.4f ", rank, array[i]);
  }
  printf("\n");
}

double f(double x) {
  return 4.0 / (1.0 + x * x);
}

int main(int argc, char** argv) {
  MPI_Init(&argc, &argv);
  int rank, size;
  MPI_Comm_rank(W, &rank);
  MPI_Comm_size(W, &size);

  double step = 1.0 / n;
  double x[n], localX[n / size];
  double locSolution = 0, solution;

  if (rank == 0) {
    double curr = 0;
    for (int i = 0; i < n; x[i++] = curr += step);
  }

  // Svako dobije jednake odsecke da sracuna delove integrala
  MPI_Scatter(x, n / size, MPI_DOUBLE, localX, n / size, MPI_DOUBLE, 0, W);

  // Racunamo delove integrala
  for (int i = 0; i < n / size; locSolution += f(localX[i++]) * step);

  // Saberemo sve delove
  MPI_Reduce(&locSolution, &solution, 1, MPI_DOUBLE, MPI_SUM, 0, W);
  if (rank == 0) printf("%.25f\n", solution);

  MPI_Finalize();
  return 0;
}