C++ for Scientists - Technische Universität Dresden

13.2. MESSAGE PASSING 261
int main (int argc, char∗ argv[])
{
MPI Init(&argc, &argv);
}
Because:
int myrank, nprocs;
MPI Comm rank(MPI COMM WORLD, &myrank);
MPI Comm size(MPI COMM WORLD, &nprocs);
float vec[2];
vec[0]= 2∗myrank; vec[1]= vec[0]+1;
// Local accumulation
float local= std::abs(vec[0]) + std::abs(vec[1]);
// Global accumulation
float global;
MPI Allreduce (&local, &global, 1, MPI FLOAT, MPI SUM, MPI COMM WORLD);
std::cout ≪ ”Hello, I am process ” ≪ myrank ≪ ” and I know too that |v| 1 is ” ≪ global ≪ ”.\n”;
MPI Finalize();
return 0 ;
• Higher abstraction:
• MPI implementation usually adapted the underlying hardware: typically logarithmic effort;
can be tuned in assember for network card