|Bill Allombert on Fri, 24 May 2013 21:51:59 +0200|
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|Re: Number of real roots of a polynomial|
On Fri, May 24, 2013 at 03:41:49PM -0400, Charles Greathouse wrote: > Given a univariate polynomial, how can I determine the number of real > solutions with gp? > > Usually I look at polroots(P) and count the number of roots which have an > imaginary part which 'looks like' 0. But I'd like a solution that certifies > that the zeros are not merely close to being real. > > A solution giving the number of distinct real roots would be equally useful > for me. Speed is important in this application, so if there's a good way to > do it with the library that would be fine (though I'm just using GP now). Assuming your polynomial is squarefree, polsturm will give you the answer. Try ???"real roots" Cheers, Bill.