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Re: Real roots of polynomials

  • To: mathgroup at
  • Subject: [mg24725] Re: Real roots of polynomials
  • From: "Allan Hayes" <hay at>
  • Date: Wed, 9 Aug 2000 02:31:24 -0400 (EDT)
  • References: <8mdl69$>
  • Sender: owner-wri-mathgroup at

How about the following?

Allan Hayes
Mathematica Training and Consulting
Leicester UK
hay at
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Jack Goldberg" <jackgold at> wrote in message
news:8mdl69$5hc at
> Hi,
> Suppose  Pn[x]  is a polynomial of degree n in x.  Its coefficients
> are real.
> Question:  What is a good way of determining the real roots of Pn
> and their multiplicities?
> Use NSolve and "cast out" the complex roots and Chop any
> roots with a "too" small imaginary part (in case NSolve
> inserts spurious imaginary parts).
> In cases where  n  is large and the number of real roots is small
> compared to  n, one can imagine that better methods exist.  I have
> searched MathSource with no real (pun intended) progress.  Possibly
> this is more a math question than a Mathematica question.
> Help is appreciated.
> Jack

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