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Re: Parculiarities of FindRoot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116082] Re: Parculiarities of FindRoot
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 1 Feb 2011 06:53:50 -0500 (EST)

On 1/31/11 at 3:24 AM, tianhuil at princeton.edu (Tianhui Li) wrote:

>Here's a question for the group: in the following function, Func
>seems to evaluate numerical arguments correctly and *works* when you
>throw it into a FindRoot.  But the second command generates a lot of
>warning messages.  Does anyone understand why?

>Func[y_] := x^2 /. FindRoot[x + y == 0, {x, 0.}]
>Func[.2]
>FindRoot[Func[z], {z, 0.}]

FindRoot is a *numeric* root finder. When you do Func[.2] you
provide a numeric value and FindRoot can find a numeric
solution. When you do FindRoot[z] you are supplying a symbolic
value and it is not possible for FindRoot to get a numeric solution.



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