[igraph] communities_spinglass original method with negative weights

[Szabolcs Horvát]

Hello,

According to the documentation, communities_spinglass doesn't support
negative weights with the original method.

http://igraph.org/c/doc/igraph-Community.html#igraph_community_spinglass

"The vector giving the edge weights, it may be NULL, in which case all
edges are weighted equally. Edge weights should be positive, altough
this is not tested."


What does this mean exactly? What happens if I pass negative weights?
In a simple test, the function return a result (both in C and R)
without complaints ("altough this is not tested").  Is the result
simply useless?

What is the rationale behind not checking the weight vector at least
in the high level interfaces?

Szabolcs