M_faisal_lab_09.docx

CSL-342: Parallel Programming lab Semester BSIT – 06 Student Name: Muhammad Faisal Registration: 43865

Lab 09: Performing Parallel Rank with MPI

Exercises Exercise 1 Write a program to finding the standard deviation of a distributed set of numbers. For those that may have forgotten, standard deviation is a measure of the dispersion of numbers from their mean. A lower standard deviation means that the numbers are closer together and vice versa for higher standard deviations. Code #include <stdio.h> #include <stdlib.h> #include <mpi.h> #include <math.h> #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]); 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(time(NULL)*world_rank); // Seed the random number generator of processes uniquely 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 <

#include <stdio.h> #include <stdlib.h> #include <mpi.h> #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]); 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(time(NULL)*world_rank); // Seed the random number generator to get different results each time for each processor float *rand_nums = NULL; rand_nums = create_rand_nums(num_elements_per_proc);

num_elements_per_proc; i++) { local_sum += rand_nums[i]; } // Reduce all of the local sums into the global sum in order to // calculate the mean float global_sum; MPI_Allreduce(&local_sum, &global_sum, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD); float mean = global_sum / (num_elements_per_proc * world_size); // Compute the local sum of the squared differences from the mean float local_sq_diff = 0; for (i = 0; i < num_elements_per_proc; i++) { local_sq_diff += (rand_nums[i] - mean) * (rand_nums[i] - mean); } // Reduce the global sum of the squared differences to the root process // and print off the answer float global_sq_diff; MPI_Reduce(&local_sq_diff, &global_sq_diff, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD); if (world_rank == 0) { float stddev = sqrt(global_sq_diff / (num_elements_per_proc * world_size)); printf("Mean - %f, Standard deviation = %f\n", mean, stddev); } // Clean up free(rand_nums); MPI_Barrier(MPI_COMM_WORLD); MPI_Finalize(); }

Output:

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(); }