On Wed, Mar 23, 2011 at 01:02:59PM +0100, Martin Rubey wrote:
> "Nicolas M. Thiery" <nicolas.thi...@u-psud.fr> writes:
>
> > The rationale for using 0,...,n-1 is that this makes the code
> > simpler and quite faster, in particular when the elements of the
> > poset are large objects with expensive hash function. That's a
> > standard approach in the Sage library (see e.g. Mike's patch to
> > have permutation groups with any domain, or Florent's
> > FiniteSetMaps).
>
> I admit that I don't *quite* understand. If I have a Poset and ask for
> it's Hasse diagram, it should not make a difference in speed or
> readability whether
>
> a) Hasse diagram internally converts to 0..n-1
>
> or
>
> b) Hasse diagram requires elements 0..n-1.
>
> (of course, the conversion should only be done once).
The rationale above is not about the hasse_diagram method. It is about
the implementation of most of the poset algorithmic, like computing
order_ideals, antichains and the like.
> OK, will do if I ever run across it, but it seems to me that either I
> have imagined it only or it was fixed recently. (looking at Mikes
> domain patch for PermGroup suggests the latter)
Ah I see now. Christian's patch on the Sage-Combinat queue was
changing the original hasse diagram method to return a graph on the
nodes 0,...,n-1. And I removed that change. Hence this discussion to
make sure we all agreed on that.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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