Re: [igraph] power.law.fit

[Gabor Csardi]

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