fork download
copy 
  1. #include <mpi.h>
  2. #include <iostream>
  3. #include <vector>
  4. #include <algorithm>
  5.  
  6.  int N = 400; // Size of the matrices (e.g., 100x100)
  7.  
  8. void printMatrix(const std::vector<std::vector<int>>& matrix, int rows, int cols) {
  9. 	for (int i = 0; i < rows; ++i) {
  10. 		for (int j = 0; j < cols; ++j) {
  11. 			std::cout << matrix[i][j] << " ";
  12. 		}
  13. 		std::cout << std::endl;
  14. 	}
  15. }
  16.  
  17. int main(int argc, char** argv) {
  18. 	MPI_Init(&argc, &argv);
  19. 	int rank, size;
  20. 	MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  21. 	MPI_Comm_size(MPI_COMM_WORLD, &size);
  22.  
  23. 	// Define matrices
  24. 	std::vector<std::vector<int>> matrix1(N, std::vector<int>(N, 1)); // Initialize with 1s for simplicity
  25. 	std::vector<std::vector<int>> matrix2(N, std::vector<int>(N, 1)); // Initialize with 1s for simplicity
  26. 	std::vector<std::vector<int>> resultMatrix(N, std::vector<int>(N, 0));
  27.  
  28. 	if (rank == 0) {
  29. 		std::cout << "Starting matrix multiplication for " << N << "x" << N << " matrices using point-to-point communication..." << std::endl;
  30. 	}
  31.  
  32. 	// Start timer after data distribution
  33. 	double start_time = MPI_Wtime();
  34.  
  35. 	// Broadcast matrix2 to all processes (all processes need matrix2 for computation)
  36. 	for (int i = 0; i < N; ++i) {
  37. 		MPI_Bcast(matrix2[i].data(), N, MPI_INT, 0, MPI_COMM_WORLD);
  38. 	}
  39.  
  40. 	// Calculate rows_per_process and start index for each process
  41. 	int rows_per_process = N / size;
  42. 	int extra_rows = N % size; // To handle cases where N is not evenly divisible by size
  43.  
  44. 							   // Assign extra row to processes if N % size != 0
  45. 	int start_row = rank * rows_per_process + std::min(rank, extra_rows);
  46. 	int end_row = start_row + rows_per_process + (rank < extra_rows ? 1 : 0);
  47.  
  48. 	// Each process calculates its assigned rows
  49. 	for (int i = start_row; i < end_row; ++i) {
  50. 		for (int j = 0; j < N; ++j) {
  51. 			resultMatrix[i][j] = 0;
  52. 			for (int k = 0; k < N; ++k) {
  53. 				resultMatrix[i][j] += matrix1[i][k] * matrix2[k][j];
  54. 			}
  55. 		}
  56. 	}
  57.  
  58. 	// Send the computed rows back to the root process (rank 0)
  59. 	if (rank == 0) {
  60. 		// Root process gathers its own rows
  61. 		for (int i = 1; i < size; ++i) {
  62. 			int start = i * rows_per_process + std::min(i, extra_rows);
  63. 			int end = start + rows_per_process + (i < extra_rows ? 1 : 0);
  64.  
  65. 			for (int j = start; j < end; ++j) {
  66. 				MPI_Recv(resultMatrix[j].data(), N, MPI_INT, i, j, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
  67. 			}
  68. 		}
  69. 	}
  70. 	else {
  71. 		// Non-root processes send their computed rows to root
  72. 		for (int i = start_row; i < end_row; ++i) {
  73. 			MPI_Send(resultMatrix[i].data(), N, MPI_INT, 0, i, MPI_COMM_WORLD);
  74. 		}
  75. 	}
  76.  
  77. 	// End timer
  78. 	double end_time = MPI_Wtime();
  79.  
  80. 	// Print the result and elapsed time in the root process
  81. 	if (rank == 0) {
  82.  
  83.  
  84. 		printMatrix(matrix1, N, N);
  85. 		printMatrix(matrix2, N, N);
  86. 		printMatrix(resultMatrix,N,N);
  87.  
  88. 		std::cout << "Matrix multiplication complete." << std::endl;
  89. 		std::cout << "Time taken: " << end_time - start_time << " seconds" << std::endl;
  90. 	}
  91.  
  92. 	MPI_Finalize();
  93. 	return 0;
  94. }
  95.  
Success #stdin #stdout #stderr 0.24s 40660KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
Standard output is empty
stderr
copy 
Error: unexpected symbol in " int N"
Execution halted
https://ideone.com/8NZJHQ
language:
R (R 3.5.2)
created:
5 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!