effect of cache demonstration

cachetest.cpp

#include <iostream>
#include <time.h>
#include <vector>
using namespace std;

int main(int argc, char **argv) {
    const int MAX = 10000;
    vector<vector<double>> A(MAX, vector<double>(MAX));
    vector<double> x(MAX), y(MAX);
    for(int i=0;i<MAX;++i) 
        for(int j=0;j<MAX;++j) A[i][j] = rand();
    for(int i=0;i<MAX;++i) x[i] = rand();

    clock_t ts, te;
    ts = clock();
    for(int i=0;i<MAX;++i) {
        for(int j=0;j<MAX;++j) {
            y[i] += A[i][j] * x[j];
        }
    }
    te = clock();
    cout << te - ts << endl;
    ts = clock();
    for(int j=0;j<MAX;++j) {
        for(int i=0;i<MAX;++i) {
            y[i] += A[i][j] * x[j];
        }
    }
    te = clock();
    cout << te - ts << endl;

    return 0;
}