       FindRoot output format

• To: mathgroup at smc.vnet.net
• Subject: [mg3425] FindRoot output format
• From: "Nicolo' Manaresi" <manaresi at iis.ee.ethz.ch>
• Date: Wed, 6 Mar 1996 01:47:15 -0500
• Organization: ETHZ
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,
I would like to define the inverse function of
f[x_] = 3*x*(1 - x^2)^(1/2) + (1 + 2 x^2)*ArcCos[-x]
(defined for x in [-1,1]).
I defined then:
finv[y_] = FindRoot[  f[x] == y,  {x,0}]

I woul like to plot it and use finv in more complex expressions,  but I have
some problem
since evaluation of  finv yeld something in the form {x -> number}
e.g.:
> finv[0.5]
> {x -> -0.363331}
So for example
> Plot[finv[y],{y,0.5,0.8}]
results in errors of this kind:
Plot::plnr: CompiledFunction[{y}, finv[y], -CompiledCode-][y]
is not a machine-size real number at y = 0.5

Does  anybody  knows how to work arond this kind of output format?
Does anybody know how could I invert f with another Mathematica's instruction,
without this problem?

Thank you,
Nicolo' Manaresi

| Nicolo` Manaresi  - Integrated Systems Laboratory - E.T.H.Z.
| ETZ-Building, Gloriastr. 35, CH-8092 Zurich, Switzerland
| Tel: ++41-1-6325345 Fax: +41-1-6321194 email: manaresi at iis.ee.ethz.ch

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