Re: [igraph] R-implementations of games

[Gábor Csárdi]

Hi,

On Mon, Feb 1, 2010 at 8:58 PM, Arthur Kaiser <address@hidden> wrote:
> Hallo,
> do R-implementations of games exist?

no, at least not within the package. There might be some code
available here and there, e.g. on this mailing list.

> I especially need a R-implementation of aging.prefatt.game.
> Here is an example of a simple barabasi.game implementation:
>
> my.ba.game<-function(n, directed){
>        graph<-graph.empty(directed)
>        graph<-add.vertices(graph, 1) #add first vertex
>
>
>    for(i in 1:n){
>        # snapshot
>        # if(i==x) {write graph}
>
>        # and the rest
>        graph<-add.vertices(graph, 1) #add a vertex
>
>        startvertices<-graph[4][[1]] #in degree

These are indeed the "incoming ends" of the edges, but I would not do
this. This is a violation of the API. Why don't you simply use an edge
list matrix in this loop (probably with pre-allocated size to save
time)? You are not really using anything igraph specific, anyway.

>        maxj<-length(startvertices)
>
>        j<-sample(1:maxj, 1)
>        vj<-startvertices[j] #to
>
>        if(maxj==0){graph<-add.edges(graph, c(i,0))
>        }else{graph<-add.edges(graph, c(i, vj))}
>
>    graph<-simplify(graph)
>    }
> return(graph)
> }
>
> Are you wondering why I ask for this? I need snapshots of the graph during
> the generation process. I also want to combine games e.g. ba with a d-dim
> latice or a randoom game without writing it in c and compile. Can someone
> help me please?

Tamás already told you about the snapshots. I'm not sure what you mean
by 'combine', but you could just create the lattice separately and
create the union of the two graphs. See e.g. graph.union.

In general, we don't want to rewrite everything in R, just to have
another implementation, so I'm afraid that you'll need to do this for
yourself. Note that the R implementations of these functions will
typically contain 'for' loops and they will be much slower than the C
versions.

Best Regards,
Gabor

> Thanks in advance.
>
> Arthur Kaiser
>
> University of Applied Sciences Brandenburg
> Faculty of Computer Science and Media
>
>
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>



-- 
Gabor Csardi <address@hidden>     UNIL DGM