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Re: [igraph] pagerank implementation questions

From: Gabor Csardi
Subject: Re: [igraph] pagerank implementation questions
Date: Tue, 6 Mar 2007 14:39:29 +0100
User-agent: Mutt/1.5.12-2006-07-14

On Mon, Mar 05, 2007 at 04:49:27PM -0800, stainless steel some one wrote:
> Thanks for all the great answers.
[... advertisement bullshit ... :) ]
> I just wonder what's the largest graph that igraph
> developers have used with igraph, and what's the
> performance of pagerank convergence speed (in
> particular)? if you can put some numbers there, it
> will be more convincing :-)

Ok, the homepage isn't completely correct. igraph can handle very large 
graphs, but only if they fit into the main memory. The principle is that
all implemented algorithm should follow the current state of the art, ie.
it should be the fastest possible. (There are some algorithms in igraph
right now which violate this principle, but for the common operations 
it is true.)

I have a graph with 7 million vertices and average degree 8 which 
i worked with quite frequently. All the basic operations are fast 
enough for interactive use. Of course you cannot do maximum flow or 
betweenness calculation with such a graph, at least not interactively.
If you think an algorithm could be significantly faster please report it, 
this is considered as a bug in igraph. :)

Summary. If your graph fits into the memory then igraph is good 
enough for you for most algorithms.

> BTW, I noticed that igraph is under GNU license. Can
> it be changed to something slightly different (e.g.
> wxWidgets Licence,
> http://wxwidgets.org/about/newlicen.htm) to allow
> binary linking with the library?  this guarantees:
> -- any enhancement to the library itself is always
> contributed back;
> -- but if an application just use igraph, it can link
> and generate a binary executable which doesn't fall
> under GPL?

Ok, this is from the wxWidgets license:

 2. The exception is that you may use, copy, link, modify and distribute
  under your own terms, binary object code versions of works based
  on the Library.

Hmmm, maybe i don't get this right, why is this good? igraph could be 
perhaps LPGL, i'll think about that.  But why the exception?
For me it seems that this exeption makes it possible to sell propriatery 
software in binary form, containing igraph or enhancements to igraph, 
without ever giving back the source to me.
Could you point me to an example? (I can imagine that the wxwidgets homepage
has lots of them.) Please consider that i'm a programmer and not a lawyer.


> =======================================================================
> -- Judging people by the non/sense he makes, not the name he bears.
> -- intelligence = openminded + compassionate
> "I don't see why the sex of the candidate is relevant -- this is after all an 
> academic institution not a bath house!" -- Hilbert on Noether's not being 
> offered a professorship from University of Göttingen.
> =======================================================================
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Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK

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