Reorganize some methods for loops

[dcoudert]

We have 2 methods for returning the loops of a (di)graph, loops and loop_edges, and one is faster than the other.

sage: G = Graph(10, loops=True)
sage: G.add_edges([(u,u) for u in G])
sage: %time L1 = G.loop_edges()
CPU times: user 68 µs, sys: 23 µs, total: 91 µs
Wall time: 73 µs
sage: %time L2 = G.loops()
CPU times: user 181 µs, sys: 50 µs, total: 231 µs
Wall time: 194 µs
sage: L1 == L2
True
sage: D = digraphs.DeBruijn(10,1)
sage: %time L1 = D.loop_edges()
CPU times: user 80 µs, sys: 18 µs, total: 98 µs
Wall time: 86.1 µs
sage: %time L2 = D.loops()
CPU times: user 333 µs, sys: 76 µs, total: 409 µs
Wall time: 344 µs
sage: L1 == L2
True

Note however that the slower (loops) has an extra parameter for edge labels. Let's try to clean that.

Component: graph theory

Author: David Coudert

Branch/Commit: fc65b8c

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/22911

[dcoudert]

comment:1

So far I have let both methods and improved the loop_edges method.

I don't know what's the best option:

1. deprecate one of the methods and ensure the fastest code is in the other one
2. make the slowest method an alias for the fastest one and so let both names

Any advice / opinion is welcome. Option 2 is the easiest one, but...

---

New commits:

1521d8e	trac #22911: reorder loop related methods
fd7bf7f	trac #22911: add parameter labels to loop_edges

[dcoudert]

Branch: u/dcoudert/22911

[dcoudert]

Commit: fd7bf7f

[tscrim]

comment:2

I would not deprecate the method, but just make loops and alias for loop_edges (with the extra parameter).

Also, while you're moving methods around in the file (something I try to avoid doing because it can create trivial conflicts easily), I would clean up the docstrings Returns -> Return and

- ``labels`` -- whether returned edges have labels (``(u,v,l)``) or not (``(u,v)``)

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

85b7ef5

trac #22911: make loops an alias for loop_edges and fix doc strings

[sagetrac-git]

Changed commit from fd7bf7f to 85b7ef5

[dcoudert]

comment:4

Should be better now.

[tscrim]

comment:5

Last thing, we should move those doctests from loops into loop_edges as they cover a few other cases now not tested (at least from looking at the diff).

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

c22c505

trac #22911: merge doctests

[sagetrac-git]

Changed commit from 85b7ef5 to c22c505

[dcoudert]

comment:7

I have merged the doctests. Some cases are may be not covered, but I don't know which one.

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:8

Hmm...maybe I misparsed the graphs in my mind. Thanks. Just remove the period in the INPUT: and you can set a positive review on my behalf.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

fc65b8c

trac #22911: remove period in input

[sagetrac-git]

Changed commit from c22c505 to fc65b8c

[dcoudert]

comment:10

Thank you Travis.

[vbraun]

Changed branch from u/dcoudert/22911 to fc65b8c