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MathGroup Archive 2001

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Re: FindRoot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31495] Re: FindRoot
  • From: <emueller at ybkim.mps.ohio-state.edu>
  • Date: Thu, 8 Nov 2001 04:54:39 -0500 (EST)
  • Organization: Ohio State University
  • References: <9sb3u5$8oc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Your function f takes on the value True if x equals i, and False if x does
not equal i.  FindRoot acts on real valued functions.  You get an error
message because neither True, nor False is a real number.

My guess is you want something like 
f[i_] := x-i
which vanishes when x=i.

Cheers,
Erich

On Wed, 7 Nov 2001 Pieter-Jan.DeSmet at fys.kuleuven.ac.be wrote:

> Dear Sir,
> 
> Can you clarify the following error message?
> 
> In[3]:= f[i_] := x == i
> 
> In[5]:= FindRoot[f[1], {x, 0}]
> 
> FindRoot::frnum: Function {False} is not a length 1 list of
> numbers at {x} = {0.}.
> 
> Out[5]=FindRoot[f[1], {x, 0}]
> 
> 
> This is a simplified version of an error message I got in a more
> difficult case. I hope that I have not made a stupid mistake.
> 
> Thank you very much
> 
> Pieter-Jan De Smet
> 
> 
> 
> 
> 
> 



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