#13006: All-paths in a graph blows up when start and end are identical vertices
--------------------------------+-------------------------------------------
Reporter: rbeezer | Owner: jason, ncohen, rlm
Type: defect | Status: positive_review
Priority: minor | Milestone: sage-5.1
Component: graph theory | Resolution:
Keywords: sd40.5 | Work issues:
Report Upstream: N/A | Reviewers: Rob Beezer
Authors: Dan Drake | Merged in:
Dependencies: | Stopgaps:
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Changes (by rbeezer):
* status: needs_review => positive_review
* reviewer: => Rob Beezer
Old description:
> Seems to be a problem for digraphs also.
>
> {{{
> sage: G = graphs.CompleteGraph(4)
> sage: G.all_paths(2,2)
> ---------------------------------------------------------------------------
> IndexError Traceback (most recent call
> last)
> <snip>
> 11495 s=act_path_iter[-1].next() # try to get the
> next neighbor/successor, ...
> 11496 except (StopIteration): # ... if there is
> none ...
> <snip>
> IndexError: list index out of range
> }}}
>
> For this trivial situation, there is no "previous" iterator. We could
> immediately return the trivial answer, or catch the exception, or place
> an empty iterator on the list.
New description:
Seems to be a problem for digraphs also.
{{{
sage: G = graphs.CompleteGraph(4)
sage: G.all_paths(2,2)
---------------------------------------------------------------------------
IndexError Traceback (most recent call
last)
<snip>
11495 s=act_path_iter[-1].next() # try to get the
next neighbor/successor, ...
11496 except (StopIteration): # ... if there is
none ...
<snip>
IndexError: list index out of range
}}}
For this trivial situation, there is no "previous" iterator. We could
immediately return the trivial answer, or catch the exception, or place an
empty iterator on the list.
'''Apply'''
1. [attachment:13006.patch]
--
Comment:
Good fix. Passes all tests in `sage/graphs` and documentation looks good.
Positive review.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13006#comment:2>
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