Le vendredi 8 janvier 2016 10:13:46 UTC+1, Johan S. R. Nielsen a écrit :
>
> The call to f.coefficients() run the following lines (self = f):
>
> tmp = {}
> for j in self._bg_value.coefficients():
> for m in j.monomials():
>
> tmp[self.parent(m)]=j.monomial_coefficient(self.parent()._poly_ring(m))
>
> I may be missing something, but it seems that instead of the inner loop,
> one could just loop over j.dict(). The values of this are already in the
> right parent. Converting the keys should not be too expensive (and would
> have to be done in any case, if one wants to use the output of
> f.polynomial().dict() while retaining the return type of
> f.coefficients()).
>
Based on tests I just did, converting the keys *is expensive* and most of
the time is taken by this operation. To my mind, the type of the keys for
the dictionary returned by the method coefficients is weird: each key is
itself a (full) multivariate power series... So the time taken by the
method is due to the initialization of many distinct power series. I would
be in favor of changing the method coefficients to make it either an alias
of the method dict, or simply return a list of coefficients (as it is the
case for multivariate polynomials).
Bruno
>
> Johan
>
>
> Ralf Stephan writes:
>
> > On Friday, January 8, 2016 at 1:51:27 AM UTC+1, Daniel Lowengrub wrote:
> >>
> >> 1) If we are just reading the coefficients of the power series, why
> should
> >> it matter if we first cast it to a polynomial?
> >>
> >
> > We are not. There are substitutions happening, leading to expensive
> > computation of powers.
> >
> >
> >> 2) If the issue lies in the details of the PowerSeries implementation,
> >> then would it make sense to simply cast powerseries to polynomials
> before
> >> calling methods that do not distinguish between the two?
> >>
> >
> > In this special case yes. I don't know for the general case.
> >
> > Regards,
>
> --
>
--
You received this message because you are subscribed to the Google Groups
"sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sage-devel+unsubscr...@googlegroups.com.
To post to this group, send email to sage-devel@googlegroups.com.
Visit this group at https://groups.google.com/group/sage-devel.
For more options, visit https://groups.google.com/d/optout.
