code example
MPI-2 message passing interface, version 2
one-sided communication defined in MPI-2
OpenMP multi-threading
Brook+ ATI GPU stream computing

#include <mpi.h>
#include <omp.h>

float e;

// kernel
kernel void sub1(float x[], float y[],
  out float xout<>, out float eout<>)
{
  // do computation
  float i = 1 + indexof(xout).x;
  xout = x[i] + (y[i+1] + y[i-1])*.5f;
  eout = y[i] * y[i];
}

reduce void sub2(float y<>, reduce float e<>)
{
  e += y;
}

int main(int argc, char *argv[]) {
  int n = ...;
  MPI_Init(&argc, &argv);
  int numproc, me;
  MPI_Comm_size(MPI_COMM_WORLD, &numproc);
  MPI_Comm_rank(MPI_COMM_WORLD, &me);
  int p_left = -1, p_right = -1;
  if (me > 0)
   p_left = me-1;
  if (me < numproc-1)
   p_right = me+1;
  int n_local0 = 1 + (me * (n-1)) / numproc;
  int n_local1 = 1 + ((me+1) * (n-1)) / numproc;
  // allocate only local part + ghost zone of the arrays x,y
  float *x, *y;
  MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
   MPI_INFO_NULL, &x);
  MPI_Alloc_mem(sizeof(float) * (n_local1 - n_local0 + 2),
   MPI_INFO_NULL, &y);
  x -= (n_local0 - 1);
  y -= (n_local0 - 1);
  MPI_Win win;
  MPI_Win_create(&y[n_local0], sizeof(float) * (n_local1-n_local0+2),
   sizeof(float), MPI_INFO_NULL, MPI_COMM_WORLD, &win);

  ... // fill x, y

  // fill ghost zone
  MPI_Win_fence(0, win);
  if (p_left != -1)
   MPI_Put(&y[n_local0], 1, MPI_FLOAT, p_left,
   n_local1-n_local0+1, 1, MPI_FLOAT, win);
  if (p_right != -1)
   MPI_Put(&y[n_local1-1], 1, MPI_FLOAT, p_right,
   0, 1, MPI_FLOAT, win);
  MPI_Win_fence(0, win);

  e = 0;
  #pragma omp parallel
  {
  int p = omp_get_thread_num();
  int num = omp_get_num_threads();
  #define BLOCK (8190)
  float xStream<BLOCK>;
  float xoutStream<BLOCK>;
  float yStream<BLOCK+2>;
  float einStream<BLOCK+2>;
  float eStream<1>;
  int n0 = 1+((n_local1-n_local0)*p)/num;
  int n1 = 1+((n_local1-n_local0)*(p+1))/num;
  float ee = 0;
  for (int i=n0; i<n1; i+=BLOCK) {
   streamRead(xStream, x+i);
   streamRead(yStream, y+i-1);
   sub1(xStream, yStream, xoutStream, einStream);
   streamWrite(xoutStream, x+i);
   sub2(einStream, eStream);
   float e_local;
   streamWrite(eStream, &e_local);
   ee += e_local;
  }
  #pragma omp atomic
  e += ee;
  }

  float e_local = e;
  MPI_Allreduce(&e_local, &e, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);

  ... // output x, e

  MPI_Win_free(&win);
  x += (n_local0 - 1);
  y += (n_local0 - 1);
  MPI_Free_mem(y);
  MPI_Free_mem(x);
  MPI_Finalize();
  return 0;
}

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