Beware of NSolve
- To: mathgroup at smc.vnet.net
- Subject: [mg50165] Beware of NSolve
- From: carlos at colorado.edu (Carlos Felippa)
- Date: Wed, 18 Aug 2004 01:20:19 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
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.
- Follow-Ups:
- Re: Beware of NSolve
- From: Murray Eisenberg <murray@math.umass.edu>
- Re: Beware of NSolve