    @Test
    public void scalarMultiply() throws Exception {

        float vec1[] = {1, 0, 0};
        float vec2[] = {0, 1, 0};
        float res = Vector3D.scalarMultiply(vec1, vec2);
        assertTrue(equal(res, 0));

        float v3[] = {5, 0, 0};
        float v4[] = {3, -1, 0};
        res = Vector3D.scalarMultiply(v3, v4);
        assertTrue(equal(res, 15));
    }