ccom3034-labExecutionTime/matrixMult.cpp

// Compare the execution times of multiplying a matrix by a vector vs
// a matrix by a matrix.
//
// Usage:
//    ./<exec name> <size of list>

#include <iostream>
#include <vector>
#include <cstdlib>
#include <algorithm>

typedef unsigned int uint;
using namespace std;

const int SIZE = 20000;

void vectorMatrixMult(const vector< vector <int> > & M, const vector<int> & y, vector<int> &res) {
	res.resize(y.size());
  for (int r = 0; r < M.size(); r++) {
    	int sum = 0;
    	for (int c = 0; c < y.size(); c++) {
        	sum = sum + (M[r][c] * y[c]);
        }
      	res[r] = sum; 
    }
}

void matrixMatrixMult(const vector< vector <int> > & A, 
  const vector< vector <int> > & B, vector< vector <int> > & res) {
  
  res.resize(A.size());
  for (auto &r: res) {
    r.resize(B[0].size());
  }

  for (uint cb = 0; cb < B[0].size(); cb++) {
    for (uint ra = 0; ra < A.size(); ra++) {
      int sum = 0;
      for (uint ca = 0; ca < A[0].size(); ca++) {
        // printf("ra ca cb: %d %d %d\n",ra,ca,cb);
          sum = sum + (A[ra][ca] * B[ca][cb]);
      }
      res[ra][cb] = sum; 
    }
  }
}



void fillMatrix(vector< vector <int> > & M, uint size) {
  M.resize(size);
  for (uint r = 0; r < size; r++) {
    M[r].resize(size);	
    for (uint c = 0; c < size; c++) {
        	M[r][c] = rand() % size;
        }
    }	
}

void fillVector(vector<int> & V, int size) {
  V.resize(size);
  for (int r = 0; r < size; r++) {
       V[r]= rand() % size;
  }	
}


int main(int argc, char *argv[]) {
  
  if (argc < 2) { 
  	cout << "Usage: " << argv[0] << " <size> \n"; 
    exit(1);
  }
  int size = atoi(argv[1]);
  
  vector< vector<int> > M;
  vector <int> x, y;
  
  srand(time(NULL));
  
  
  fillMatrix(M,size);
  fillVector(y,size);
  

  double elapsed_secs;

  // measure vector matrix mult time
  clock_t begin = clock();
  vectorMatrixMult(M, y, x);
  clock_t end = clock();

  elapsed_secs = static_cast<double>(end - begin) / CLOCKS_PER_SEC;
  cout << "\nTime elapsed for vector matrix mult: " << elapsed_secs << " seconds\n";
  
  // measure matrix matrix mult time
  vector < vector <int> > R;
  begin = clock();
  matrixMatrixMult(M,M,R);
  end = clock();

  elapsed_secs = static_cast<double>(end - begin) / CLOCKS_PER_SEC;
  cout << "Time elapsed for matrix matrix mult: " << elapsed_secs << " seconds\n\n";
    
  return 0;
}