On 4/17/2013 5:32 AM, Rupert Swarbrick 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 it is the MAIN variable, yes. It is the ?cadadr(p). It can be made
the main variable by
rat(p, x) even if p is in cRE form with another main variable.
If it is not the main variable, a search is necessary, e.g. hipow of y
in (y+1)*x^10 + (y^2+4)*x^9 + (y^100+3)*x...
It seems to me that somewhere there is a routine (not directly a user
command) that
picks out high power, which is needed, for example, to do division with
remainder.
RJF