Sloan ordering does not work on disconnected graphs

[Jeroen Meijer <jjgmeijer@…>]

The Sloan ordering algorithm in graph/sloan_ordering.hpp does not work for disconnected graphs.

This can be easily confirmed by running an example of a graph with two disconnected vertices.

The attached file simply creates a graph with two vertices without any edges. Running the attached file yields:

i: 0
i: 0

The result should be:

i: 0
i: 1

Or the result should be:

i: 1
i: 0

The problem also holds for larger disconnected graphs.