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## Re: [igraph] What exactly does igraph_transitivity_undirected() compute

 From: Szabolcs Horvát Subject: Re: [igraph] What exactly does igraph_transitivity_undirected() compute for directed graphs? Date: Mon, 7 Dec 2015 14:28:43 +0100

```Thanks again for the clarification!  I think what actually happens is
that the neighbours of a vertex are counted as the degree of that
vertex (which is not the same thing for multigraphs).

Do you think a patch that converts directed graphs to undirected
simple graphs before computing the local clustering coefficient would
be appropriate here?

On 7 December 2015 at 13:16, Gábor Csárdi <address@hidden> wrote:
> I am not sure if it is defined. I guess this is just a case when the
> behavior is not defined for multi-graphs.
>
> Gabor
>
> On Mon, Dec 7, 2015 at 12:14 PM, Szabolcs Horvát <address@hidden> wrote:
>> Thank you for the explanation.
>>
>> Could you elaborate a bit on how igraph defines the local clustering
>> coefficient when multiple (parallel) edges are present?
>>
>> On 7 December 2015 at 12:56, Gábor Csárdi <address@hidden> wrote:
>>> It's because of the multiple edges in the first graph. I.e.:
>>>
>>>> transitivity(as.undirected(g, mode = "each"),"local")
>>> [1] 0.3333333 0.3333333 1.0000000
>>>
>>> Gabor
>>>
>>> On Mon, Dec 7, 2015 at 10:05 AM, Szabolcs Horvát <address@hidden> wrote:
>>>> Hello,
>>>>
>>>> What precisely does igraph_transitivity_undirected() compute for
>>>> directed graphs?
>>>>
>>>> The C documentation states that
>>>>
>>>> "Directed graphs are considered as undirected ones."
>>>>
>>>> but this is not exactly the case.
>>>>
>>>> With an example using the R interface (for simplicity),
>>>>
>>>>> g<-make_graph(c(1,2, 2,1, 2,3, 3,1))
>>>>> transitivity(g,"local")
>>>> [1] 0.3333333 0.3333333 1.0000000
>>>>
>>>>> transitivity(as.undirected(g),"local")
>>>> [1] 1 1 1
>>>>
>>>> Can someone clarify what precisely is computed in the directed case?
>>>>
>>>> Szabolcs
>>>>
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