Subject: finding roots of polynomials with high precision
From: Barton Willis
Date: Sun, 5 Sep 2010 12:21:58 -0500
To find the big float roots of a polynomial, use the function bfallroots:
(%i1) bfallroots(x^5-x+1=0,x), fpprec : 50;
(%o1) [x=3.5247154603172624931794709140258105439420648082425b-1*%i+7.648844336005 < junk deleted> ]
I think find_root uses double floats, not big floats. Thus bfloat(find_root(g(x),x,-2,-1))
computes the roots using doubles and then converts the doubles to big floats.
--Barton
-----maxima-bounces at math.utexas.edu wrote: -----
>In?Maple?I?can?find?the?real?root?of?x^5-x+1?to?50?decimal?places?like
>this:
>
>evalf(solve(x^5-x+1=0,x),50);
>-1.1673039782614186842560458998548421807205603715255
>
>How?do?I?do?this?in?Maxima?
>
>I?tried?this?but?got?the?wrong?answer:
>
>fpprec:?50;
>g(x):=bfloat(x^5-x+1);
>bfloat(find_root(g(x),x,-2,-1));
>(%o14)??????-?1.1673039782614187398479543844587169587612152099609b0
>
>
>
>
>??????
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