MPI Program using MPI_Scatter and MPI_Reduce - parallel-processing

Question

Write an MPI program that efficiently compute the sum of array elements.
Program 1: Tasks communicate with MPI_Scatter and MPI_Reduce.
The programs can assume that the number of processes is a power of two.
The programs should add 2^15 = 65536 random doubles in the range 0 to 100.
Task 0 must generate the numbers, store them in array and distribute them to the tasks.
Each task does a serial sum of the numbers it is assigned. The local sums are then
added together using a tree structured parallel sum.
After the parallel sum is complete, task 0 should compute a serial sum of the
same numbers (to verify the result).
Task 0 must print the parallel sum, the serial sum and the time required for the
parallel sum (including data distribution).

Answer 1

#include <stdio.h>
#include <mpi.h>
int main(int argc,char *argv[]){
MPI_Init(NULL,NULL); // Initialize the MPI environment
int rank;
int comm_size;
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
MPI_Comm_size(MPI_COMM_WORLD,&comm_size);
int number1[2];
int number[4];
if(rank == 0){
number[0]=1;
number[1]=2;
number[2]=3;
number[3]=4;
//number[4]=5;
}
double local_start, local_finish, local_elapsed, elapsed;
MPI_Barrier(MPI_COMM_WORLD);
local_start = MPI_Wtime();
//All processes
MPI_Scatter(number, 2, MPI_INT, &number1, 2, MPI_INT, 0, MPI_COMM_WORLD);
//printf("I'm process %d , I received the array : ",rank);
int sub_sum = 0;
for(int i=0 ; i<2 ; i++){
// printf("%d ",number1[i]);
sub_sum = sub_sum + number1[i];
}
printf("\n");
int sum = 0;
MPI_Reduce(&sub_sum, &sum, 1, MPI_INT, MPI_SUM,0,MPI_COMM_WORLD);
local_finish = MPI_Wtime();
local_elapsed = local_finish -local_start;
MPI_Reduce(&local_elapsed,&elapsed,1,MPI_DOUBLE,MPI_MAX,0,MPI_COMM_WORLD);
if(rank == 0)
{
printf("\nthe sum of array is: %d\n",sum);
printf("Elapsed time = %e seconds\n",elapsed);
}
MPI_Finalize();
return 0;
}