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Re: [igraph] python igraph bug

From: jujulj
Subject: Re: [igraph] python igraph bug
Date: Fri, 23 Nov 2007 13:36:03 +0100

I used eigenvector based community detection.

On Nov 22, 2007 7:16 PM, Tamas Nepusz <address@hidden> wrote:
> Hi,
> I think the bug is unrelated to getting a nonexistent edge:
>  >>> from igraph import *
>  >>> g=Graph(10000)
>  >>> g.get_eid(500, 600)
> Traceback (most recent call last):
>    File "<stdin>", line 1, in ?
> igraph.core.InternalError: Error at igraph/type_indexededgelist.c:
> 1019: Cannot get edge id, no such edge, Invalid value
> According to the backtrace, igraph is trying to free an invalid
> pointer which is accidentally left in the "finally" stack (used to
> emulate exception handling behavior in C the layer). Since the
> "finally" stack is cleared when igraph returns an error, the error
> message that's usually shown when getting a nonexistent edge triggers
> the error, but it is not the main cause. I'm almost sure about this,
> since igraph_get_eid (the underlying C function) does not use the
> "finally" stack at all. (For more details on the "finally" stack,
> please refer to the documentation of the C core, especially to the
> chapter about error handling). It also seems that the pointer that's
> left in the stack once belonged to an adjacency list view of the graph
> since igraph is trying to free it by igraph_i_adjlist_destroy. So the
> question is: what methods did you call before you encountered this
> error and which ones can be somehow connected to an adjacency list
> view? I checked the source code and it seems that the following
> methods use igraph_i_adjlist_destroy:
> - functions related to cliques and maximal independent vertex sets
> - eigenvector based community detection
> - minimum cut calculation
> - Reingold-Tilford layout
> - RAND-ESU motif detection and triad census (yet unimplemented in the
> Python interface)
> - diameter, average path length, Pagerank calculation
> - random rewiring
> - transitivity
> --
> T.
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