Re: Beware of NSolve
- To: mathgroup at smc.vnet.net
- Subject: [mg50181] Re: [mg50165] Beware of NSolve
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Thu, 19 Aug 2004 06:28:12 -0400 (EDT)
- Organization: Mathematics & Statistics, Univ. of Mass./Amherst
- References: <200408180520.BAA06016@smc.vnet.net>
- Reply-to: murray at math.umass.edu
- Sender: owner-wri-mathgroup at wolfram.com
But:
NSolve[f == 0, x, WorkingPrecision -> 32]
{{x -> -0.014126116704662366388244906316568},
{x -> 0.0028165928951385568644353825070445}}
Carlos Felippa wrote:
> Run v. 4.2 on Mac:
>
> f=5/432 - 11/(27*Sqrt[70]*Sqrt[19 - 1890*x]) + x/(2*Sqrt[38/35 - 108*x]);
>
> Solve[f==0,x] returns 2 real roots:
>
> {{x -> (-171 - 25*Sqrt[105])/30240}, {x -> (-171 + 25*Sqrt[105])/30240}}
>
> NSolve[f==0,x] returns 4 real roots:
>
> {{x -> -0.10481082961146104}, {x -> -0.014126116704662378},
> {x -> 0.002816592895138556}, {x -> 0.0003796126802330315}}
>
> Roots 1 and 4 are incorrect. (Just plot f)
>
> Had a similar problem with a quartic 3 months ago. This is a
> simpler example.
>
>
--
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305
- References:
- Beware of NSolve
- From: carlos@colorado.edu (Carlos Felippa)
- Beware of NSolve