Call function in indexController from another controller Zend

Call function in indexController from another controller Zend

Need to call some function from another controller (not IndexController),
for example:
class IndexController extends Zend_Controller_Action
{
public function indexAction()
{
$someFunction = new CustomController();
$someFunction->someFunc();
}
} But this throws an error :
Fatal error: Class 'CustomController' not found in
C:\xampp\htdocs\demo.ru\application\controllers\IndexController.php on
line 13