Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2004

[Date Index] [Thread Index] [Author Index]

Search the Archive

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.


  • Prev by Date: Licence manager network connections
  • Next by Date: GUIKit: Color?
  • Previous by thread: Re: Licence manager network connections
  • Next by thread: Re: Beware of NSolve