/**
* Add a new edge.
*
* @param Vertex $vertex The 'from' vertex
* @param Vertex $toVertex The 'to' vertex
*
* @return Edge
*/
public function addEdge($vertex, $toVertex)
{
$edge = $vertex->createEdgeTo($toVertex);
$edge->setLayoutAttribute('shape', 'none');
$edge->setLayoutAttribute('fontname', 'Arial');
$edge->setLayoutAttribute('fontsize', '12');
return $edge;
}