/* Global error */
MPI_Reduce(&error, &global_error, 1, MPI_FLOAT, MPI_MAX, 0, MPI_COMM_WORLD);
// broadcast global error so that everyone enters the next iteration with the same error
MPI_Bcast(&global_error, 1, MPI_FLOAT, 0, MPI_COMM_WORLD);
error = global_error;