Real solving univariate polynomials in an extension field
Δημοσιεύθηκε από nostart στο Απριλίου 25, 2007
Recently I am interested in studying the algorithmic and implementation details of the problem of isolating the real (and if possible the complex) roots of univariate polynomials with coefficients in an a single extension field. Moreover, I am considering exact algorithms only, i.e. algorithms that allow only operations with integers of arbitrary bit size.
I am considering the easy case, where the coefficients of the polynomial, say , are depending on one real algebraic number, say
, i.e.
, where
is the variable. The number
is in isolating interval representation, i.e.
, hence in order to represent it, we use a square-free polynomial,
, and an isolating interval that contains
and no other real root of
. Let
is the degree of
and
be the maximum bit size of the coefficients of
.
It seems that there are two approaches to our problem:
- Compute a polynomial with integer coefficients that has as roots the roots of
(and probably other roots as well) and solve it.
- Apply to the well known algorithms for univariate real root isolation, e.g. Sturm, Descarte, Bernstein, CF, to
, suitably modified so that to work with polynomials with real algebraic numbers as coefficients.
What is the best way from a theoretical and an implementation point of view, in order to isolate the real roots of $f$? Is there any other approach different from the ones mentioned above?