public void testEquals() {        
        // default instances
        Vector v1 = new Vector(1.0, 2.0);
        Vector v2 = new Vector(1.0, 2.0);
        assertTrue(v1.equals(v2));
        assertTrue(v2.equals(v1));

        v1 = new Vector(1.1, 2.0);
        assertFalse(v1.equals(v2));
        v2 = new Vector(1.1, 2.0);
        assertTrue(v1.equals(v2));
        
        v1 = new Vector(1.1, 2.2);
        assertFalse(v1.equals(v2));
        v2 = new Vector(1.1, 2.2);
        assertTrue(v1.equals(v2));