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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. int main() {
  5.     long long N = 10000000;
  6.  
  7.     // Simulate running with 4 virtual MPI ranks
  8.     int simulated_size = 4; 
  9.     long long total_sum = 0;
  10.  
  11.     std::cout << "--- Simulating MPI Cluster with " << simulated_size << " Ranks ---" << std::endl;
  12.  
  13.     for (int rank = 0; rank < simulated_size; rank++) {
  14.         // Your exact distribution formulas
  15.         long long start = rank * N / simulated_size + 1;
  16.         long long end = (rank + 1) * N / simulated_size;
  17.         long long local_sum = 0;
  18.  
  19.         // Each simulated rank does its chunk
  20.         for (long long i = start; i <= end; i++) {
  21.             local_sum += i;
  22.         }
  23.  
  24.         std::cout << "Simulated Process " << rank
  25.                   << ": start = " << start
  26.                   << ", end = " << end
  27.                   << ", local sum = " << local_sum
  28.                   << std::endl;
  29.  
  30.         // Simulating the MPI_Reduce behavior (global accumulation)
  31.         total_sum += local_sum;
  32.     }
  33.  
  34.     std::cout << "\n[Rank 0 Emulated Output]:" << std::endl;
  35.     std::cout << "Final sum = " << total_sum << std::endl;
  36.  
  37.     return 0;
  38. }
Success #stdin #stdout 0.01s 5320KB
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stdin
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Standard input is empty
stdout
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--- Simulating MPI Cluster with 4 Ranks ---
Simulated Process 0: start = 1, end = 2500000, local sum = 3125001250000
Simulated Process 1: start = 2500001, end = 5000000, local sum = 9375001250000
Simulated Process 2: start = 5000001, end = 7500000, local sum = 15625001250000
Simulated Process 3: start = 7500001, end = 10000000, local sum = 21875001250000

[Rank 0 Emulated Output]:
Final sum = 50000005000000
https://ideone.com/aTFLCo
language:
C++ (gcc 8.3)
created:
4 days ago
visibility:
public

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