Exactly, no disrep of CREs is needed for hipow/lopow. It's a little more
complicated than ?cadadr, but not much, for rational functions, for taylor
series, etc.
-s
On Wed, Apr 17, 2013 at 8:32 AM, Rupert Swarbrick <rswarbrick at gmail.com>wrote:
> Stavros Macrakis <macrakis at alum.mit.edu> writes:
> > Well, if you're going to do the (grossly inefficient) hipow, then you
> > don't need the p:p-r*v^i at all -- you can just pick off the ratcoefs
> > directly. And of course you don't re-rat each time -- I was assuming
> poly:
> > rat(input_poly,x)$
> >
> > I agree about something like
> >
> > rat_hipow(p,x):= ?cadadr(rat(p,x))
> >
> > (with a bit of care for the edge and error cases). My question was
> > whether there already existed something like that or close to it.
>
> Assuming not, would it make sense for hipow to be made more efficient
> when dealing with expressions in CRE form?
>
> Quickly thinking about it, hipow doesn't need to disrep something in CRE
> form at all: If the variable we're interested in is one of the variables
> in the car then we can just read the answer off. If not, presumably we
> can just take the maximum power over the arguments (since we're looking
> at a sum and we only care about powers in the coefficients). Am I
> missing something?
>
> Rupert
>
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