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#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// it is a message passing interface
// processes live inside a COMM_WORLD
// processes are LIVING, and exist in a COMMUNICATOR
int main(int argc, char **argv)
{
// start the MPI code
MPI_Init(NULL, NULL);
int num_procs; // to store the size of the world / num of procs
MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
int rank;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (rank == 0)
{
// read the array
int n;
printf("Enter number of elements : ");
scanf("%d", &n);
int arr[n];
for (int i = 0; i < n; i++)
{
arr[i] = rand() % 10000 + 1
}
printf("Array is -\n [ ");
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("]\n");
int elem_to_send = n / 2;
if (n % 2)
elem_to_send++;
// send the size
MPI_Send(&elem_to_send, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
// send the array
MPI_Send(&arr[n / 2], elem_to_send, MPI_INT, 1, 1, MPI_COMM_WORLD);
float t1 = clock();
int local = 0;
for (int i = 0; i < n / 2; i++)
local = local + arr[i];
int s_rec = 0;
float t2 = clock();
printf("Time taken by process %d : %f\n", rank, (t2 - t1) / CLOCKS_PER_SEC);
// recv the data into the local var s_rec
MPI_Recv(&s_rec, 1, MPI_INT, 1, 2, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
local = local + s_rec;
printf("Total sum of array is %d\n", local);
}
else
{
// recieve the size of elements
float t1 = clock();
int size;
MPI_Recv(&size, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
int arr[size];
MPI_Recv(arr, size, MPI_INT, 0, 1, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
float t2 = clock();
printf("Total time for recieving : %f", (t2 - t1) / CLOCKS_PER_SEC);
// lol, the time for recieving the elements is a thousand times slower
// than the processing, lol waste
t1 = clock();
int local = 0;
for (int i = 0; i < size; i++)
local = local + arr[i];
printf("\nProcess %d sending sum %d back to main...\n", rank, local);
t2 = clock();
printf("Time taken by process for addition %d : %f\n", rank, (t2 - t1) /
CLOCKS_PER_SEC);
MPI_Send(&local, 1, MPI_INT, 0, 2, MPI_COMM_WORLD);
}
MPI_Finalize();
}