Add Ver Simple Implementation of the Naive MPI Allreduce

MPI_Allrduce.c

+#include <mpi.h>
+#include <iostream>
+#include <vector>
+#include <cstdlib>
+#include <ctime>
+
+using namespace std; 
+
+// Naïve implementation of MPI_Allreduce
+void naive_allreduce(int local_value, int& global_value, MPI_Comm comm) {
+
+    int rank, size;
+    MPI_Comm_rank(comm, &rank);
+    MPI_Comm_size(comm, &size);
+
+    // to store values from all processes
+    vector<int> all_values(size, 0);
+    
+    // [1] Send the local value to all processes
+ 
+    for (int i = 0; i < size; i++) {
+        if (i != rank) {
+            MPI_Send(&local_value, 1, MPI_INT, i, 0, comm);
+        }
+    }
+
+    // [2] Receive values from all processes
+
+    // Store own value first
+    all_values[rank] = local_value; 
+    // Recieve the values from other process
+    for (int i = 0; i < size; i++) {
+        
+        // to avoid recive value from the process itself 
+        if (i != rank) {
+            // Revieve the value gfrom rnal i 
+            MPI_Recv(
+                &all_values[i],
+                1, 
+                MPI_INT, 
+                i, 0, 
+                comm, 
+                MPI_STATUS_IGNORE
+            );
+        }
+    }
+
+    // [3] Perform reduction (sum)
+
+    // global value 
+    global_value = 0;
+
+    for (int i = 0; i < size; i++) {
+        //reduction 
+        global_value += all_values[i];
+    }
+}
+
+int main(int argc, char** argv) {
+
+    // init 
+    MPI_Init(&argc, &argv);
+
+    int rank, size;
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+    MPI_Comm_size(MPI_COMM_WORLD, &size);
+
+    // Initialize local values
+
+    // Seed with time and rank for unique values
+    srand(time(0) + rank); 
+
+    // Random integer between 0 and 99 (this is first simple intutyion in the next stage i will replace it with array )
+    int local_value = rand() % 100; 
+
+    // Print local values for each process
+   printf("[Worker @ %d] I has local value: %d \n",rank,local_value );
+
+    //[1] Use the naive implementation of MPI_Allreduce
+    int global_value_naive = 0;
+    naive_allreduce(local_value, global_value_naive, MPI_COMM_WORLD);
+    printf("[Worker @ %d] I received global sum (naive): %d \n",rank, global_value_naive);
+
+    // [2] Use the built-in MPI_Allreduce for comparison
+    int global_value_builtin = 0;
+    // Mpi Alllreduce buld in
+    MPI_Allreduce(
+        &local_value,
+        &global_value_builtin,
+        1, MPI_INT, 
+        MPI_SUM, 
+        MPI_COMM_WORLD
+    );
+
+    printf("[Worker @ %d] I received global sum (MPI_Allreduce): %d \n" ,rank, global_value_builtin );
+
+    // Fina;ize 
+    MPI_Finalize();
+    return 0;
+}