// Author: Wes Kendall // Copyright 2013 www.mpitutorial.com // This code is provided freely with the tutorials on mpitutorial.com. Feel // free to modify it for your own use. Any distribution of the code must // either provide a link to www.mpitutorial.com or keep this header in tact. // // Program that computes the average of an array of elements in parallel using // MPI_Reduce. // #include #include #include #include #include // Creates an array of random numbers. Each number has a value from 0 - 1 float *create_rand_nums(int num_elements) { float *rand_nums = (float *)malloc(sizeof(float) * num_elements); assert(rand_nums != NULL); int i; for (i = 0; i < num_elements; i++) { rand_nums[i] = (rand() / (float)RAND_MAX); } return rand_nums; } int main(int argc, char** argv) { if (argc != 2) { fprintf(stderr, "Usage: avg num_elements_per_proc\n"); exit(1); } int num_elements_per_proc = atoi(argv[1]); // Seed the random number generator to get different results each time srand(time(NULL)); MPI_Init(NULL, NULL); int world_rank; MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); int world_size; MPI_Comm_size(MPI_COMM_WORLD, &world_size); // Create a random array of elements on all processes. srand(world_rank); float *rand_nums = NULL; rand_nums = create_rand_nums(num_elements_per_proc); // Sum the numbers locally float local_sum = 0; int i; for (i = 0; i < num_elements_per_proc; i++) { local_sum += rand_nums[i]; } // Print the random numbers on each process printf("Local sum for process %d - %f, avg = %f\n", world_rank, local_sum, local_sum / num_elements_per_proc); // Reduce all of the local sums into the global sum float global_sum; MPI_Reduce(&local_sum, &global_sum, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD); // Print the result if (world_rank == 0) { printf("Total sum = %f, avg = %f\n", global_sum, global_sum / (world_size * num_elements_per_proc)); } // Clean up free(rand_nums); MPI_Barrier(MPI_COMM_WORLD); MPI_Finalize(); }