I am not sure if these are strictly adhered to in visualizepanel
so I am making them private to avoid confusion, (note that they will
be correct in this class, VLINE and HLINE aren't used).
This is an event which is fired by a LayoutEngine once
a LayoutEngine finishes laying out the graph, so
that the Visualizer can repaint the screen to show
the changes.
This method does a complete layout of the graph which includes
removing cycles, assigning levels to nodes, reducing edge crossings
and laying out the vertices horizontally for better visibility.
Find a new point x in the direction p from a point xold at which the
value of the function has decreased sufficiently, the positive
definiteness of B matrix (approximation of the inverse of the Hessian)
is preserved and no bound constraints are violated.