This method can be overridden to customize the layout algorithm, but care should be taken to ensure that each node and link in the input network are properly initialized and terminated. If Network is null, one is automatically allocated and initialized with the graph that is in the Document. After all of the computations are completed, this calls LayoutNodesAndLinks in order to commit the positions of all of the nodes. No undo/redo transaction is started or finished by this method.