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MathGroup Archive 2001

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Re: FindRoot

  • To: mathgroup at
  • Subject: [mg31484] Re: [mg31463] FindRoot
  • From: Mianlai Zhou <lailai at>
  • Date: Thu, 8 Nov 2001 04:54:19 -0500 (EST)
  • Sender: owner-wri-mathgroup at


It is because that FindRoot has an attribute HoldAll, i.e., it will not
evaluate its arguments until it starts to try to find the roots (replacing
x by number). Therefore, you have to change as follows to get what you

In[5]:= FindRoot[Evaluate @ f[1], {x, 0}]

Good luck!

Mianlai Zhou
Theory Group, NIKHEF
Amsterdam, the Netherlands

On Wed, 7 Nov 2001 Pieter-Jan.DeSmet at 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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