public function crossProduct(Vector $mult)
{
$cx = $this->get_y() * $mult->get_z() - $this->get_z() * $mult->get_y();
$cy = $this->get_z() * $mult->get_x() - $this->get_x() * $mult->get_z();
$cz = $this->get_x() * $mult->get_y() - $this->get_y() * $mult->get_x();
$dest = new Vertex(array('x' => $cx, 'y' => $cy, 'z' => $cz));
$prod = new Vector(array('dest' => $dest));
return $prod;
}
private function _translate(Vector $v)
{
$this->_matrix['x']['w'] += $v->get_x();
$this->_matrix['y']['w'] += $v->get_y();
$this->_matrix['z']['w'] += $v->get_z();
}