is_line_graph() bug

[赵日天]

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)

<ipython-input-6-a5cd36160d42> in <module>()

      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?

[Dima Pasechnik]

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


>
> --
> You received this message because you are subscribed to the Google Groups "sage-devel" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+...@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/e2941e84-c1f8-48f5-adea-7a0b18353868o%40googlegroups.com.