public static double[][] multiply2(double[][] m1, double[][] m2) {
        double[][] temp = new double[4][4];
        for (int i = 0; i < 4; i++)
            for (int j = 0; j < 4; j++)
                temp[i][j] = (m2[i][0] * m1[0][j]) + (m2[i][1] * m1[1][j])
                        + (m2[i][2] * m1[2][j]) + (m2[i][3] * m1[3][j]);
        return temp;
    }