On Sat, Jun 27, 2020 at 10:35 AM 赵日天 wrote:
>
> While running the code
>
> for g in graphs():
> print(g.is_line_graph())
>
> Sage returns the error message, after lots of True-s and False-s:
>
> ---
> Exception Traceback (most recent call last)
> in ()
> 1 for g in graphs():
> > 2 print(g.is_line_graph())
> 3
>
> /opt/sagemath-9.0/local/lib/python3.7/site-packages/sage/graphs/line_graph.pyx
> in sage.graphs.line_graph.is_line_graph
> (build/cythonized/sage/graphs/line_graph.c:2286)()
> 220 if g.is_connected():
> 221 try:
> --> 222 R, isom = root_graph(g)
> 223 if certificate:
> 224 return True, R, isom
>
> /opt/sagemath-9.0/local/lib/python3.7/site-packages/sage/graphs/line_graph.pyx
> in sage.graphs.line_graph.root_graph
> (build/cythonized/sage/graphs/line_graph.c:7147)()
> 621
> 622 if not is_isom:
> --> 623 raise Exception(error_message)
> 624
> 625 return R, isom
>
> Exception: It looks like there is a problem somewhere. Youfound a bug here !
> Please report it on sage-devel,our google group !
>
> What's the bug here?
A bug in is_line_graph() has recently been fixed here:
https://trac.sagemath.org/ticket/29740
This fix should be in Sage 9.2.beta2
>
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