Re: [igraph] problems in generating scale-free networks

[Mario Lavezzi]

Hello Gàbor

it works!

thank you very much (and excuse me for this late reply, but I wanted to 
do many attempts)

Mario

Gábor Csárdi wrote:
> Mario, try to generate denser graphs, this can be done independently
> of the exponent of the power-law degree distribution.
> E.g. simply
>
> degs <- degs * 2
>
> might be enough if you don't care about not having vertices with degree 1.
>
> G.
>
> On Tue, Oct 21, 2008 at 12:39 PM, Mario Lavezzi <address@hidden> wrote:
>   
> > Hi
> >
> > I need to generate scale-free networks with different exponents.
> >
> > Following previous suggestions by Gabor, I am using these commands
> >
> > degs <- sample(1:n, n, replace=TRUE, prob=(1:n)^(-scale))
> >   if (sum(degs) %% 2 != 0) { degs[1] <- degs[1] + 1 }
> >   g5 <- degree.sequence.game(degs, method="vl")
> >   all(degree(g5) == degs)
> >
> > where "scale" is my exponent (set by me, along with other parameters).--
> >
> > So far, I have simulated networks with 2000 agents and, with parameters
> > between 2 and 2.5 I did not find particular problems in obtaining a network
> > structure.
> >
> > However, I noticed that, moving from 2.5 to higher values, the algorithm
> > finds more and more difficult to generate a network structure, and I get the
> > message:
> >
> > graph::make_connected() failed : #edges < #vertices-1
> > Errore in degree.sequence.game(degs, method = "vl") :
> >  At gengraph_mr-connected.cpp:141 : Cannot make a connected graph from the
> > given degree sequence, Invalid value
> >
> > So far, I have tried to circumvent this by changing the seed of the random
> > generator with the instruction:
> >
> > mySeed=33
> > set.seed(mySeed, kind = NULL)
> >
> > I change the "mySeed" parameter and restart the program, until the algorithm
> > works and a network is generated.
> >
> > However, with exponents >= 2.5 it takes a very high number of attempts to
> > get it to work.
> >
> > I tried with higher (or much higher) numbers of agents, but it seems that
> > little changes.
> >
> > I would like to reach an exponent of about 3, 3.2.
> >
> > Any suggestion?
> >
> > Thanks to all
> > Mario
> >
> > Andrea Mario Lavezzi
> > Dipartimento di Studi su Politica, Diritto e Società
> > Università di Palermo
> > Piazza Bologni 8
> > 90134 Palermo, Italy
> > tel. ++39 091 6625600
> > fax ++39 091 6112023
> > skype: lavezzimario
> > email: lavezzi (at) unipa.it
> > web: http://www.unipa.it/~lavezzi
> >
> >
> >
> > _______________________________________________
> > igraph-help mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/igraph-help
> >
> >     
>
>
>
>   

--
Andrea Mario Lavezzi
Dipartimento di Studi su Politica, Diritto e Società
Università di Palermo
Piazza Bologni 8
90134 Palermo, Italy
tel. ++39 091 6625600
fax ++39 091 6112023
skype: lavezzimario
email: lavezzi (at) unipa.it
web: http://www.unipa.it/~lavezzi