Hi Nicolas,
I'm assuming the subject line got your attention. :) I've been working
on a basic implementation of quasisymmetric functions (monomial and
fundamental basis only, no Hopf operations) and I already have something
that seems to work. Without using sage-combinat. Hooray! Three cheers
for categories in sage!
I did find a couple of questions as I went through this exercise,
though. As you might guess, I looked at ncsf for a model. In the
combinat/ncsf directory of sage-combinat, there is a file called
categories.py. My questions are about three classes defined in this file:
Category_concrete_representation
ConcreteRepresentations and
Bases
The first two seem to not be specific to NCSF at all, and I ended up
just copy-pasting them into them into my file. This isn't so good,
since I would never have figured out to write them without ncsf as a
guide. Is there a reason they aren't in sage-main? Can we put them in
somewhere?
The third one, as I understand it, defines the category of bases of a
given instance of NCSF. I'm interested in the relation between this and
the class 'Basis' in nscf.py, which inherits from
CombinatorialFreeModule. A specific basis (say, Phi) will inherit from
Basis, and be assigned the category Bases(NCSF). Currently, Bases
contains a section
class ParentMethods:
which defines an attribute 'basis_indices', as well as the method
'one_basis()' and a few auxiliary methods relating to changing bases.
It took me some time to figure out what was going on here (I'm still not
completely sure I understand how ParentMethods works), and I would have
much preferred to find these functions in the Basis class. In my
implementation of QSym, I avoided using 'ParentMethods' altogether by
putting all the code in the corresponding Basis class, and everything
seems to work. Am I missing something? 'ParentMethods' feels like
sneaking code in through the back door, and while I accept that it may
sometimes be necessary, I think I would like to personally avoid it, if
I can. Can I? :)
Thanks,
Jason
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