[igraph] Question about assortativity

[Marcel Salathé]

Hi

I've got a question about assortativity based on continuous values assigned to 
vertices (i.e. the assortativity function).

I'm curious how vertices are assumed to be of the same value if values are 
continuous. I couldn't find anything in the documentation. Looking up Newman's 
paper (Mixing patterns in networks, p.5) I found the following "By analogy with 
the developments of Section II, we can define a quantity exy, which is the 
fraction of all edges in the network that join together vertices with values x 
and y for the age or other scalar variable of interest. The values x and y 
might be either discrete in nature (e.g., integers, such as age to the nearest 
year) or continuous (exact age), making exy either a matrix or a function of 
two continuous variables. Here, for simplicity, we concentrate on the discrete 
case, but generalization to the continuous case is straightforward."

What function is igraph using to determine if two continuous values are of the 
same "type"?

Thanks for clarification
Marcel