On Thu, Feb 16, 2012 at 11:54:56PM -0800, Anne Schilling wrote:
> Thank you so much! So that I understand for the future: __init__ always needs
> to take parent as an input for the element class?
Indeed.
> But it does not need to take all inputs that would be needed for a
> class call?
More precisely, class call may encode the inputs in a different form;
in your case, the parent contains the information about the poset.
> Why did the parent method in this case also need a
> __classcall_private__? Is it because of the optional variables that
> are passed in?
In part. But more importantly because LinearExtensionsOfPoset accepts
a list as input, and lists are not hashable. So class call needs to
transform it into a tuple before passing it down to
UniqueRepresentation. See the documentation of UniqueRepresentation
for details.
> Currently sage seems to randomly choose a linear extension for a
> given poset. However, it is much nicer if the specified poset P
> corresponds to the identity linear extension.
Ok. Then don't we want instead to be able to specify a linear
extension to the Poset constructor?
Say:
sage: P = Poset(...., linear_extension = [1,2,3,4,5,6,7])
Which could be used as well to change the default linear extension:
sage: Q = Poset(P, linear_extension = [1,3,2,5,4,6,7])
Also we might want to have Poset be clever enough to test if the list
of vertices provided by the user is a linear extension, and if it is
to use it as default linear extension rather than looking for some
random one?
> I do not find it so unnatural to have P.linear_extension() and
> P.linear_extensions(). If P.linear_extensions() becomes the list of
> LinearExtensionsOfPoset, then what should linear_extension become? I
> as a user would prefer to assign the identity to P as a linear
> extension.
I am a bit confused now. I guess part of the question is whether we
want to have a double use for P.linear_extension:
sage: P.linear_extension()
returns the default linear extension of P (as a list or as a linear
extension?)
sage: P.linear_extension([1,5,3])
returns the linear extension [1,5,3]
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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