Matrix.java

class Matrix {
    public static void main(String args[]) {
        if (args.length != 1) {
            System.out.println("usage: java Matrix N");
            return;
        }
        int n = Integer.parseInt(args[0]);

        double[][] a = new double[n][n]; // Matrix A
        double[][] b = new double[n][n]; // Matrix B
        double[][] c = new double[n][n]; // Matrix C

        // Initialize the matrices to some values.
        int i, j;
        for (i = 0; i < n; i++) {
            for (j = 0; j < n; j++) {
                a[i][j] = i * n + j;
                b[i][j] = j * n + i;
                c[i][j] = 0;
            }
        }

        long begin = System.currentTimeMillis();
    
    int k;
    for (i=0; i<n; i++){
        for (j=0; j<n; j++){
           for (k=0; k<n; k++){
               c[i][j]+=a[i][k]*b[k][j];
           }
        }
    }
    

        long end = System.currentTimeMillis();
        System.out.printf("time: %.6f sec\n", (end - begin) / 1000.0);

        // Print C for debugging. Comment out the print before measuring the execution
        // time.
        double sum = 0;
        for (i = 0; i < n; i++) {
            for (j = 0; j < n; j++) {
                sum += c[i][j];
                // System.out.printf("c[%d][%d]=%f\n", i, j, c[i][j]);
            }
        }
        // Print out the sum of all values in C.
        // This should be 450 for N=3, 3680 for N=4, and 18250 for N=5.
        System.out.printf("sum: %.6f\n", sum);
    }
}