Re: NonlinearFit of an "implicit" function
- To: mathgroup at smc.vnet.net
- Subject: [mg94383] Re: NonlinearFit of an "implicit" function
- From: dh <dh at metrohm.com>
- Date: Thu, 11 Dec 2008 07:26:37 -0500 (EST)
- References: <gho399$77$1@smc.vnet.net>
Hi Kretch,
if I understand correctly, you have numerical values for x,y,z,f[x,y,z],
but symbolically, you have f only implicitely?
Under this assumtptions, you may write the implicite expression in the
form: G[x,y,z,f]==0.
Using the numerical values for f you can get numerical values for G.
With this you create data tuples: {x,y,z,G}. Against these, you can fit
(e.g. using Fit) the symbolllical expression G[x,y,z,ff] where ff is an
Ansatz for f.
hope this helps, Daniel
kretch wrote:
> Hi All
> I need to perform a non linear fit of a function which is not provided
> directly i.e. instead of the function having the explicit form
> f(x,y,z) = ...
> I have an implicit form
> 1/(f(x,y,z) + x^2)^3 = ...
>
> Now, I know I can manipulate the function so that I get an explicit
> form, but since I have a variety of functions (>100), this would be
> very tedious and error-prone.
>
> So my question is this:
> I'd like to get the explicit form of the function by "Solve" ing it,
> then run the fit on the explicit form. But for some reason, the exact
> syntax eludes me and I get error messages.
>
> Can somebody share an example of fitting an implicit function?
>
> Thanks
> Kretch
>
>