Re: [igraph] Translate code from r to python

[Tamas Nepusz]

Hi Simone,

> TypeError: argument 1 must be list, not int
> WARNING: Failure executing file: <analisi_venezia.py>
>
> is this a correct solution?
>
> g_sw = Graph.Lattice([1, g.vcount()], nei=sum(g.degree())/ 
> g.vcount(), dir=True, mutual=True)
Well, it depends on what you want to do. Graph.Lattice([1,  
g.vcount()]) practically generates a 1-dimensional lattice (a path, or  
a circle if you specify mutual=True). The first argument of  
Graph.Lattice describes the size of the lattice along each dimension.  
If you want to make a roughly 2D square lattice, you have to take the  
square root of g.vcount() and use that twice: [int(g.vcount()**0.5),  
int(g.vcount()**0.5)]. Note that the number of vertices will match  
g.vcount() only approximately if g.vcount()**0.5 is not an integer  
itself. If you are aiming for something like Watts and Strogatz have  
done in their original paper, then go for a 1-dimensional, mutual,  
circular lattice. See help(Graph.Lattice) for more information.

> If I understand the rewire procedure correctly, it changes in this  
> case the 25% of the edges in the graph.
More precisely: it makes 0.25*g.ecount() rewire attempts, preserving  
the degree distribution, but it does not guarantee that  
0.25*g.ecount() _unique_ edges will be rewired. Some edges might be  
rewired twice or more.

> How can it be that the average path after the rewire is longer than  
> in the regular lattice???
Is it a directed or an undirected lattice? If directed, it can happen  
easily: rewiring some of the edges almost surely breaks the reciprocal  
edge pairs by moving only _one_ of the edges. If the being moved went  
originally from A to B, then the shortest path from A to B may have  
increased from 1.

By the way, if you only need the average path length, you can simply  
use g.average_path_length().

--
Tamas