Re: Beware of NSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg50249] Re: Beware of NSolve*From*: mathma18 at hotmail.com (Narasimham G.L.)*Date*: Mon, 23 Aug 2004 06:34:11 -0400 (EDT)*References*: <cfuq2n$64h$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Old version 2.2 does not report roots 1 and 4 by NSolve. May be later on improvements (complex roots) have associated problems, may be elimination of extraneous roots by plotting is a necessary check. carlos at colorado.edu (Carlos Felippa) wrote in message news:<cfuq2n$64h$1 at smc.vnet.net>... > 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.