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  1. #include <iostream>
  2. #include <cmath>
  3. #include <mpi.h>
  4. #include <vector>
  5.  
  6. // Function to compute the value of the function f(x)
  7. double f(double x) {
  8.     return log(x) - (1.0 / 8.0) * x * x;
  9. }
  10.  
  11. // Function to compute the derivative f'(x)
  12. double f_prime(double x) {
  13.     return 1.0 / x - (1.0 / 4.0) * x;
  14. }
  15.  
  16. // Function to compute the integrand sqrt(1 + (f'(x))^2)
  17. double integrand(double x) {
  18.     double fp = f_prime(x);
  19.     return sqrt(1 + fp * fp);
  20. }
  21.  
  22. // Function to perform the Riemann sum in parallel using MPI
  23. double riemann_sum(double a, double b, int n, int rank, int size) {
  24.     double h = (b - a) / n;
  25.     double local_sum = 0.0;
  26.  
  27.     for (int i = rank; i < n; i += size) {
  28.         double x_i = a + i * h;
  29.         local_sum += integrand(x_i);
  30.     }
  31.  
  32.     double global_sum = 0.0;
  33.     MPI_Reduce(&local_sum, &global_sum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
  34.  
  35.     return global_sum * h;
  36. }
  37.  
  38. int main(int argc, char *argv[]) {
  39.     MPI_Init(&argc, &argv);
  40.  
  41.     int rank, size;
  42.     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  43.     MPI_Comm_size(MPI_COMM_WORLD, &size);
  44.  
  45.     double a = 1.0;
  46.     double b = 6.0;
  47.     int n = 100000000;  // 1.e8 partition points
  48.     if (argc > 1) {
  49.         n = std::stoi(argv[1]);
  50.     }
  51.  
  52.     double start_time = MPI_Wtime();
  53.     double length = riemann_sum(a, b, n, rank, size);
  54.     double end_time = MPI_Wtime();
  55.  
  56.     if (rank == 0) {
  57.         std::cout << "Length of the curve: " << length << std::endl;
  58.         std::cout << "Time taken: " << end_time - start_time << " seconds" << std::endl;
  59.     }
  60.  
  61.     MPI_Finalize();
  62.     return 0;
  63. }
  64.  
Success #stdin #stdout #stderr 0.26s 40868KB
comments (?)
stdin 
Standard input is empty
stdout 
Standard output is empty
stderr 
Error: unexpected '/' in "/"
Execution halted
https://ideone.com/erNzze
language:
R (R 3.5.2)
created:
169 days ago
visibility:
public

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