Re: [igraph] igraph_community_leading_eigenvector_step implementation

[Al]

Gabor,
Thanks! Now I see that igraph_i_community_leading_eigenvector_step is
being called. Thanks again for your guidance!
Thanks, Al

On Sat, Jan 10, 2009 at 1:20 PM, Gábor Csárdi <address@hidden> wrote:
> On Sat, Jan 10, 2009 at 7:09 PM, Al <address@hidden> wrote:
>> Gabor
>> igraph_community_leading_eigenvector has its own step function.
>
> Not really. igraph_i_community_leading_eigenvector_step is actually
> called by igraph_community_leading_eigenvector_step (implicitly). Just
> like igraph_i_community_leading_eigenvector is called by
> igraph_community_leading_eigenvector. But these functions do not
> calculate modularity, at least not explicitly, all they do is
> multiplying the modularity matrix by a given vector. This is the only
> required step for ARPACK to find the leading eigenvector.
>
> Btw. these (igraph_i_community_leading_eigenvector and
> igraph_i_community_leading_eigenvector_step) are exactly the functions
> where the substantial modifications should be made for adding edge
> weights; the modularity matrix is defined by them.
>
> Gabor
>
>> Please
>> refer line 1276 of the communities.c R package source file.
>> Thanks, Al
>>
>>
>> On Sat, Jan 10, 2009 at 1:04 PM, Gábor Csárdi <address@hidden> wrote:
>>> Al, as far as I can see both these functions do the same. The
>>> modularity is not explicitly calculated, but according to the original
>>> paper, and also http://arxiv.org/abs/physics/0602124 the leading
>>> eigenvector of the modularity matrix will be negative if the split
>>> would decrease the modularity, and in this case we don't split.
>>>
>>> I don't really know what difference you can see between the two
>>> functions, but I coded these quite a while ago, so can't remember all
>>> the details, so I might be wrong.
>>> Where does igraph_community_leading_eigenvector calculate the modularity?
>>>
>>> Best,
>>> Gabor
>>>
>>> On Sat, Jan 10, 2009 at 6:06 PM, Al <address@hidden> wrote:
>>>> Hi
>>>>
>>>> I am a developer tasked with generalizing the implementation of the M.
>>>> Newman community detection algorithm to accept weighted edges. We want
>>>> to use the step wise variation of the function (located in
>>>> communities.c under the igraph_community_leading_eigenvector_step
>>>> function). On inspection of the source code, it is not obvious to me
>>>> that he modularity calculation is actually being preformed. However,
>>>> in the non-step was variation of the function
>>>> (igraph_community_leading_eigenvector), I notice that it is properly
>>>> implemented. So I am wondering if the step wise variation is properly
>>>> implemented? and if so maybe some insight could be shed on where it is
>>>> preforming the M. Newman modularity calculation.
>>>>
>>>> Thanks
>>>> Al Tucker
>>>>
>>>>
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>>>>
>>>
>>>
>>>
>>> --
>>> Gabor Csardi <address@hidden>     UNIL DGM
>>>
>>>
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>>
>>
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>
>
>
> --
> Gabor Csardi <address@hidden>     UNIL DGM
>
>
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