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Re: nested findroot

• To: mathgroup at smc.vnet.net
• Subject: [mg122802] Re: nested findroot
• From: Ray Koopman <koopman at sfu.ca>
• Date: Fri, 11 Nov 2011 04:53:05 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <j9genv$p2n$1@smc.vnet.net>

On Nov 10, 4:06 am, Anna McCuan <anna.mcc... at gmail.com> wrote:
> I'm getting an error finding a root using functions which are defined
> using findroot.  This happens in spite of the fact that I can graph
> the function and see clearly that there is an easy to find root.
> Does anyone know how to execute this root search successfully?
>
> The file is posted publicly at
> http://www.math.gatech.edu/~mccuan/temp/problem.nb

Change the definitions of f and g so that
they apply only when the argument is numeric:

f[w_?NumericQ] := ...
g[w_?NumericQ] := ...

FindRoot[g[soln] - 9 f[soln] == 0, {soln, .13}]
{soln -> 0.131216}