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MathGroup Archive 2004

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Re: Problem with Mathematica driving me nuts

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46837] Re: Problem with Mathematica driving me nuts
  • From: lalu_bhatt at yahoo.com (Bhuvanesh)
  • Date: Tue, 9 Mar 2004 19:57:52 -0500 (EST)
  • References: <c2he1m$ahd$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

bpw67deletethis at hotmail.com (benwoodward.com) wrote:
> FindRoot[x^2 == 4x - 4, {x, 1}]
> 
> Out[4]=
> {x -> 1.99902}
> 
> In[15]:=
> FindRoot[x^2 - 4*x + 4, {x, 3}]
> 
> Out[15]=
> {x -> 2.00098}
> 
> When the root is clearly two.
> Is Mathematica using Newton's Method like a Ti-92?
> Even if so, why wont it give a more accurate answer?
> I've tried N[%,30] but it doesn't do anything.
> I'm new to Mathematica coming over from a Ti-92, so everything is
> frustrating right now.
> Thanks.

If you give the above initial guesses to nSolve() (on a TI-68k
calculator), you'll see that it returns 1.999999865 and 2.00000014254,
respectively. Since you're using numerical root-finding methods, the
answer will almost always be approximate.

--
Bhuvanesh,
Wolfram Research

Disclaimer: Any opinions expressed herein are my own and not
necessarily those of Wolfram Research.


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