#17711: Pre-processing for vertex separation
-------------------------+-------------------------------------------------
Reporter: | Owner:
dcoudert | Status: needs_info
Type: | Milestone: sage-6.5
enhancement | Resolution:
Priority: minor | Merged in:
Component: graph | Reviewers:
theory | Work issues:
Keywords: | Commit:
Authors: David | f62716539aaf4c236041d1e31dbf59bcb8bba750
Coudert | Stopgaps:
Report Upstream: N/A |
Branch: |
public/17711 |
Dependencies: |
#17647 |
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Comment (by dcoudert):
Replying to [comment:5 ncohen]:
> Yooooooooooooo !
>
> Does the job, very few comments (and a small commit at `public/17711b`):
>
>
> - Calling `is_strongly_connected` is very cheap while
> `g.strongly_connected_components_digraph` actually copies the whole
graph
>
> {{{
> sage: g=digraphs.DeBruijn(5,3)
> sage: %timeit g.is_strongly_connected()
> 10000 loops, best of 3: 129 µs per loop
> sage: %timeit g.strongly_connected_components_digraph()
> 1000 loops, best of 3: 1.31 ms per loop
> }}}
>
> Better to only copy it if necessary.
>
> - Is there any reason why you only deal with digraphs ? `Digraph(G)`
(when `G`
> is a graph) is not always strongly connected: `G` may not be
connected. The
> same code could handle everything at once, couldn't it ?
So you propose that I
1. test if the graph is connected. If not, then apply the algorithm on
each connected component.
2. If G is directed, test if is strongly connected. If not, then apply the
algorithm on each scc
Is that correct?
> - (unrelated) what on earth is this `random_DAG` function doing in the
global
> namespace instead of being in `digraphs.<tab>` ? `O_O`
I had the same remark while reviewing patch #12181 (and certainly other
tickets). Nothing has been done since. I don't even know where is the
code.
In fact, we have many random<TAB> stuff in global namespace...
David.
--
Ticket URL: <http://trac.sagemath.org/ticket/17711#comment:6>
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