On Sat, Apr 18, 2015 at 12:10:47PM -0700, 'Martin R' via sage-combinat-devel
wrote:
> Sorry, I should have made myself clearer: I do not understand the
> design decision behind the way map_coefficients works.
> Shouldn't it rather check whether the function actually produces
> something in the coefficient ring?
That's the usual speed vs safety vs flexibility. We definitely want to
have a fast map_coefficients that does no check, for those cases where
we know that f is an endofunction as specified by the
documentation. In some cases the user can find it handy to abuse the
system a bit (like Mike is doing), just for output. In all other cases
it would be preferable to have systematic checks.
Supporting both speed vs safety boils down to adding an option
`check=True`, and if possible going trough the Sage code and setting
`check=False` wherever we know we are on the safe side. It's an easy
change. Volunteers welcome!
For supporting cleanly Mike's needs for flexibility, we really would
need to change the base ring. It would be nice to have some idiom
like:
sage: f.map_coefficients(factor, codomain=SR)
or
sage: f.change_base_ring(SR).map_coefficients(factor)
This one is a bit trickier.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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