MPI Parallel summation of two vectors - c

Question

It is necessary to sum two vectors on separate processes in parts. I find a portion of vectors that needs to be sent out and send it using MPI_Send. Next, I summarize the parts of the vectors on the processes, I succeeded.
It is not possible to collect the resulting array again on the zero process. As far as I understand, you need to use MPI_Isend.
#include <iostream>
#include <stdio.h>
#include <mpi.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
void Print(int *vector, int n, int start) {
for (int i = start; i < n; i++)
printf("%4d", vector[i]);
}
void RandomFill(int *vector, int n) {
for (int i = 0; i < n; i++)
vector[i] = rand() % 100;
}
//C = A + B
int main(int argc, char* argv[])
{
int ProcNum, ProcRank;
MPI_Status status;
MPI_Request request;
int *A, *B, *C, *buf;
int nResult = 0;
int n = 5 + rand() % (25 - 5 + 1);
bool yes = true;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &ProcNum);
MPI_Comm_rank(MPI_COMM_WORLD, &ProcRank);
if (ProcRank == 0) {
int part_send = 0;
A = new int[n];
B = new int[n];
C = new int[n];
RandomFill(A, n);
RandomFill(B, n);
printf("\nProcess number: %d\t n = %d", ProcRank, n);
printf("\nVector A:\n");
Print(A, n, 0);
printf("\nVector B:\n");
Print(B, n, 0);
int rest = n % (ProcNum - 1);
int *rest_array = new int[rest];
printf("\n\nRest = %d", rest);
if (rest != 0)
{
part_send = (n - rest) / (ProcNum - 1);
nResult = ProcNum;
int j = 0;
for (int i = n - rest; i < n; i++) {
rest_array[j] = A[i] + B[i];
j++;
}
}
else
{
nResult = ProcNum - 1;
part_send = n / (ProcNum - 1);
}
for (int i = 1; i < ProcNum; i++)
{
int index = (i - 1) * part_send;
MPI_Send(&A[index], part_send, MPI_INT, i, 1, MPI_COMM_WORLD);
MPI_Send(&B[index], part_send, MPI_INT, i, 1, MPI_COMM_WORLD);
}
printf("\n\n");
buf = new int[part_send];
for (int i = 1; i < ProcNum; i++) {
MPI_Irecv(&buf, part_send, MPI_INT, MPI_ANY_SOURCE, 3, MPI_COMM_WORLD, &request);
if (MPI_Wait(&request, &status) == MPI_SUCCESS) {
for (int j = 0; j < part_send; j++)
C[(part_send * i) + j] = buf[j];
printf("Result:");
Print(C, n, 0);
}
}
}
else
{
printf("\n Process number: %d\n", ProcRank);
int nRecv = 0;
MPI_Probe(0, 1, MPI_COMM_WORLD, &status);
MPI_Get_count(&status, MPI_INT, &nRecv);
int *recvArr1 = new int[nRecv];
int *recvArr2 = new int[nRecv];
int *recvArrSum = new int[nRecv];
MPI_Recv(recvArr1, nRecv, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);
MPI_Recv(recvArr2, nRecv, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);
for (int i = 0; i < nRecv; i++) {
recvArrSum[i] = recvArr1[i] + recvArr2[i];
}
printf("recvArrSum:\n");
Print(recvArrSum, nRecv, 0);
MPI_Isend(&recvArrSum, nRecv, MPI_INT, 0, 3, MPI_COMM_WORLD, &request);
}
MPI_Finalize();
return 0;
}