Resultant patch

[Richard B. Kreckel]

Ralf,

On Sun, 20 Jun 2004, Ralf Stephan wrote:
> Please include. This works with any polynomial.

Hmm, this ties in with the discussion we had with Chris about expand()
inside series expansion and certain cancellations.  In your code below, I
think an unexpanded polynomial a or b would lead to some bloat because of
the problems with degree/ldegree discussed so far.  In Ginsh:

> ldegree((x+2)*(x+2)*(x+2) - (2+x)*(4+x),x);
0
> ldegree(expand((x+2)*(x+2)*(x+2) - (2+x)*(4+x)),x);
1

Methinks you should just call expand inside resultant().  Note that on
large expanded polynomials, expand is an O(1) operation due to the
expanded flag.

Also, I think the statement "Resultants are commutative" ought to be
clarified just a little bit.

Regards
    -richy.
-- 
Richard B. Kreckel
<http://www.ginac.de/~kreckel/>