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Simone Tripodi commented on SANDBOX337:

Thanks for the patch! :)
I'm not sure the modification you are proposing is 100% right, looks like for Directed graphs
there are different opinions: take a look at this [articlehttp://www.utm.edu/departments/math/graph/glossary.html]:
{quote}
*degree*
The degree (or valence) of a vertex is the number of edge ends at that vertex. For example,
in this graph all of the vertices have degree three.
In a digraph (directed graph) the degree is usually divided into the indegree and the outdegree
(*whose sum is the degree* of the vertex in the underlying undirected graph).
{quote}
Take also a look at this [sampleshttp://reference.wolfram.com/mathematica/ref/VertexDegree.html]
with directed graphs: for Vertex {{2}}, that has {{deg+ = 2}} and {{deg = 1}}, the degree
is {{2}}
In the [bookhttp://www.algoritmica.org/] I'm reading (sorry, in Italian only) it is reported
the following:
{quote}
Il grado in uscita di un nodo è pari al numero di archi uscenti da esso, mentre il grado
in ingresso e dato dal numero di archi entranti. Il grado è la somma del grado d'ingresso
e di quello d'uscita
{quote}
> Wrong value for Vertex degree
> 
>
> Key: SANDBOX337
> URL: https://issues.apache.org/jira/browse/SANDBOX337
> Project: Commons Sandbox
> Issue Type: Bug
> Components: Graph
> Reporter: Marco Speranza
> Priority: Minor
> Attachments: VertexDegreeTestCase.patch
>
>
> Hi folk, I'm doing a tests case for the class BaseMutableGraph, in order to upgrade our
testcase suite. I think that our implementation of vertex degree is wrong.
> according with http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Adjacency_and_degree
> "The degree, or valency, dG(v) of a vertex v in a graph G is the number of edges incident
to v, with loops being counted twice. A vertex of degree 0 is an isolated vertex. A vertex
of degree 1 is a leaf. In the labelled simple graph example, vertices 1 and 3 have a degree
of 2, vertices 2, 4 and 5 have a degree of 3, and vertex 6 has a degree of 1. If E is finite,
then the total sum of vertex degrees is equal to twice the number of edges."
> so for a complete graph with 5 nodes, each vertex has a degree of 4. Instead our implementation
returns 8.
> IMHO this is wrong. WDYT?
> Have a nice week end

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