Re: [igraph] power.law.fit

[Simone Gabbriellini]

Gabor,

you are right: my graphs are 25 "shots" in the evolution of one  
online community, measured using its forum communications.
the first graph has 59 nodes, the last 571.

I see the evolution of this community is scale free, and I am looking  
for some way to prove it, like power.law.fit().

I would like to plot for each graph the degree distribution and the  
fit, but I don't know how..
I need a plot with, on the x axis, the degree value, and on the y  
axis the number of nodes that hold that degree value.

I tried with degree.distribution, but I am sorry I don't understand  
the meaning of the results..

thanks,
Simone



Il giorno 03/set/07, alle ore 22:18, Gabor Csardi ha scritto:

> Simone, i don't know your graphs, but yes, i guess that you should
> only fit the tail, at least this works for the "standard" BA model:
>
> > g <- barabasi.game(100000)
> > res <- power.law.fit(degree(g), xmin=20)
> > res
>
> Call:
> mle(minuslogl = mlogl, start = list(alpha = start))
>
> Coefficients:
>    alpha
> 2.945498
>
> power.law.fit seems to work fine in general:
>
> > prob <- (1:10000)^-2.5
> > data <- sample(1:10000, 1000, replace=TRUE, prob=prob)
> > power.law.fit(data)
> Call:
> mle(minuslogl = mlogl, start = list(alpha = start))
>
> Coefficients:
>    alpha
> 2.516897
>
> You might want to plot the degree distribution and the fit.
> Also, see ?"mle-class" for more information about the actual fit.
>
> G.
>
> On Mon, Sep 03, 2007 at 05:51:18PM +0200, Simone Gabbriellini wrote:
> > dear list,
> >
> > I've used the function power.law.fit in this way:
> >
> > c<-degree(myGraph);
> > pwl<-power.law.fit(c+1);
> >
> > for a list of 25 graphs. Now I have values in the range 1,296295  
> > to 1,805046.
> >
> > I see that the value usually expected goes between 2 to 3 for real  
> > networks...
> > can you help me understand my results? maybe I have to specify the  
> > xmin value?
> > being under 2 means something particular?
> >
> > thanks a lot,
> > simone
>
> > _______________________________________________
> > igraph-help mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/igraph-help
>
>
> --
> Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK
>
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/igraph-help