On Fri, Aug 27, 2010 at 1:08 PM, Marco Rofei <marco.rofei at gmail.com> wrote:
> Hi everyone, i think there is a bug in line_graph() function.
> I tried it with some adjacency-matrix.
>
> Here an example.
>
> This is one of the matrix i used
>
> 0 1 0 0 0 1 0 0
> 1 0 1 1 0 0 0 0
> 0 1 0 0 0 1 0 0
> 0 1 0 0 1 0 1 0
> 0 0 0 1 0 1 0 0
> 1 0 1 0 1 0 0 1
> 0 0 0 1 0 0 0 1
> 0 0 0 0 0 1 1 0
>
> a:from_adjacency_matrix (read_matrix("...path..."));
> is_planar(a);
> ->true
> la:line_graph(a);
> is_planar(la);
> ->false
>
> i think this line_graph should be planar..
Why do you believe it should be planar? I think that the line graph is
computed correctly and is it is not planar (you have a vertex of
degree 4 which gives K_4 in the line graph, from there it is easy to
see that there will be a K_5 minor in the line graph).
Andrej