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[mathcad] Re: Polyroots function
| [mathcad] Re: Polyroots function |
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Author: Pergande, Albert N
Posted: Tue, 14 Jan 2003 08:15:19 -0500
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Well, it LOOKS way off, but then your leading coef is on the order of 10^18,
so you ARE getting down into the digital noise of the algorithm.
Symbolically, those coefficients give roots of -1, -1/2, -1/3..., so
something else weird is going on here...
Albert N Pergande
Senior RF Engineer
Lockheed Martin Missiles and Fire Control
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5600 Sand Lake Road Orlando Fl 32819
voice 407-356-5169
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-----Original Message-----
From: Magnus Eklund />
Sent: Tuesday, January 14, 2003 7:53 AM
To: Mathcad Discussion List
Subject: [mathcad] Re: Polyroots function
Something like this?
/Magnus
(The file is made with mc11beta2 and saved as mc2k.)
On Tue, 14 Jan 2003, Chris Whitford wrote:
> The roots of a high-order polynomial can be very sensitive to the values
of
> the coefficients. The classic example, often quoted, is to form the
> polynomial whose roots are -1,-2,...-19,-20 by direct multiplication, then
> try to solve for the roots. Depending on the machine precision, they can
be
> way off. I can't find a simple way to construct the polynomial in Mathcad,
> so I tried it in Matlab (there's a challenge for someone). The biggest
> error is the root at -14, which comes out at -14.068, even though the
> machine precision is 15 digits.
>
> Chris Whitford
>
> At 11:11 13/01/2003 +0100, you wrote:
> > I am testing the polyroots mathcad function to understand if I can
> > trust in
> >it or not. I am interested in the solution of a polynomial equation with
high
> >degree and I am interested also in the complex solutions.
> >
> > p(X) = 0
> >
> >.....
> >Alberto Borboni, Mechanical Engineer
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