#17225: Degrees of looped *immutable* graphs are wrong
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Reporter: | Owner:
kcrisman | Status: needs_review
Type: | Milestone: sage-6.4
defect | Resolution:
Priority: major | Merged in:
Component: graph | Reviewers:
theory | Work issues:
Keywords: | Commit:
Authors: | 58cf24722664d1b299ab4de934455579125e3326
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
u/ncohen/17225 |
Dependencies: |
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Comment (by kcrisman):
> HMmmmmm... Well, the thing is that it depends on what you want the
degree to be. If you want the degree of a vertex to be equal to the number
of edges incident to it, then it is correct.
> >
> > If you want the number of edges to be twice the sum of degrees, then
it is wrong.
See [http://en.wikipedia.org/wiki/Loop_(graph_theory) here] and
[http://en.wikipedia.org/wiki/Degree_(graph_theory)#cite_note-1 here],
which ''claim'' that this is a standard convention. I don't recall ever
hearing a different convention for loops either, and for directed
situations we should still be correct, right? Let me know if I'm missing
a controversy on this - sometimes there are mutually incompatible
definitions, most notoriously in my own classes for $\mathbb{N}$.
--
Ticket URL: <http://trac.sagemath.org/ticket/17225#comment:9>
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