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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <mpi.h>
  4.  
  5. #define N 1000000 // Number of random numbers in total
  6.  
  7. int compare(const void *a, const void *b) {
  8.     return (*(double*)a > *(double*)b) - (*(double*)a < *(double*)b);
  9. }
  10.  
  11. int main(int argc, char *argv[]) {
  12.     int rank, size;
  13.     double *global_data = NULL;
  14.     double *local_data;
  15.     int local_n;
  16.     double start_time, end_time;
  17.  
  18.     MPI_Init(&argc, &argv);
  19.     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  20.     MPI_Comm_size(MPI_COMM_WORLD, &size);
  21.  
  22.     local_n = N / size;  // Number of elements per process
  23.     if (N % size > rank) {
  24.         local_n++;
  25.     }
  26.  
  27.     local_data = (double *)malloc(local_n * sizeof(double));
  28.  
  29.     // Root process generates the full data set
  30.     if (rank == 0) {
  31.         global_data = (double *)malloc(N * sizeof(double));
  32.         srand(0); // Use a fixed seed for reproducibility
  33.         for (int i = 0; i < N; i++) {
  34.             global_data[i] = (double)rand() / RAND_MAX;
  35.         }
  36.     }
  37.  
  38.     // Distribute portions of the array to all processes
  39.     if (rank == 0) {
  40.         // Calculate displacements and counts for distribution
  41.         int *displs = malloc(size * sizeof(int));
  42.         int *sendcounts = malloc(size * sizeof(int));
  43.         int disp = 0;
  44.         for (int i = 0; i < size; i++) {
  45.             sendcounts[i] = N / size;
  46.             if (i < N % size) sendcounts[i]++;
  47.             displs[i] = disp;
  48.             disp += sendcounts[i];
  49.         }
  50.  
  51.         MPI_Scatterv(global_data, sendcounts, displs, MPI_DOUBLE, local_data, local_n, MPI_DOUBLE, 0, MPI_COMM_WORLD);
  52.  
  53.         free(displs);
  54.         free(sendcounts);
  55.     } else {
  56.         MPI_Scatterv(NULL, NULL, NULL, MPI_DOUBLE, local_data, local_n, MPI_DOUBLE, 0, MPI_COMM_WORLD);
  57.     }
  58.  
  59.     // Sort local data
  60.     qsort(local_data, local_n, sizeof(double), compare);
  61.  
  62.     // Gather sorted data back at root
  63.     if (rank == 0) {
  64.         int *recvcounts = malloc(size * sizeof(int));
  65.         int *displs = malloc(size * sizeof(int));
  66.         int disp = 0;
  67.         for (int i = 0; i < size; i++) {
  68.             recvcounts[i] = N / size;
  69.             if (i < N % size) recvcounts[i]++;
  70.             displs[i] = disp;
  71.             disp += recvcounts[i];
  72.         }
  73.  
  74.         MPI_Gatherv(local_data, local_n, MPI_DOUBLE, global_data, recvcounts, displs, MPI_DOUBLE, 0, MPI_COMM_WORLD);
  75.  
  76.         // Sort the entire array at root
  77.         qsort(global_data, N, sizeof(double), compare);
  78.  
  79.         free(recvcounts);
  80.         free(displs);
  81.     } else {
  82.         MPI_Gatherv(local_data, local_n, MPI_DOUBLE, NULL, NULL, NULL, MPI_DOUBLE, 0, MPI_COMM_WORLD);
  83.     }
  84.  
  85.     // Print results if needed
  86.     if (rank == 0) {
  87.         for (int i = 0; i < N; i++) {
  88.             printf("%f ", global_data[i]);
  89.         }
  90.         printf("\n");
  91.         free(global_data);
  92.     }
  93.  
  94.     free(local_data);
  95.     MPI_Finalize();
  96.     return 0;
  97. }
  98.  
Success #stdin #stdout #stderr 0.36s 40448KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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Error: unexpected symbol in "int compare"
Execution halted
https://ideone.com/Jgqncn
language:
R (R 3.5.2)
created:
11 days ago
visibility:
public

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