[vtkusers] How to make a filter operate on either mutable directed or mutable undirected graph

[Jeff Baumes]

> I want am trying to make a filter that computes and adds a weight
> array to either a vtkMutableUndirectedGraph or a
> vtkMutableDirectedGraph. The filter derives from vtkGraphAlgorithm. It
> seems like in the RequestDataObject I need to decide the type of the
> output

...

vtkGraphAlgorithm already implements RequestDataObject to do just what
you want. It will create the same type of graph on output as in the
input. The NewInstance() call in
vtkGraphAlgorithm::RequestDataObject() accomplishes this.

Jeff