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## Re: [igraph] power.law.fit

 From: Simone Gabbriellini Subject: Re: [igraph] power.law.fit Date: Tue, 4 Sep 2007 11:43:22 +0200

```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

```
```
```
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--
Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK

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