Re: Impedance Equation fit to Complex Data
- To: mathgroup at smc.vnet.net
- Subject: [mg86509] Re: Impedance Equation fit to Complex Data
- From: dh <dh at metrohm.ch>
- Date: Wed, 12 Mar 2008 05:29:41 -0500 (EST)
- References: <fr7opm$39a$1@smc.vnet.net>
Hi Benji,
there seems to be a bug in FindFit. It works if you specify the error
function explicitely:
err[x_]:=Norm[x,2];
FindFit[Data,Z,{R,G,H},w,NormFunction->err]
please inform Wolfram about this bug.
hope this helps, Daniel
AgustusBenjamin at gmail.com wrote:
> Dear Group,
>
> I'm trying to fit an equation to data using FindFit. When I type
> in the equation and data and then FindFit, I get this:
>
> Z := [Omega]^(-(2 ArcTan[H/G])/[Pi]) (G - i H) + R
>
> Data := {{1.`, 2.658637`- 8.389573` i}, {1.5`,
> 1.784396`- 6.214955` i}, {2.5`,
> 1.656569`- 3.97147` i}, {3.5`,
> 1.633799`- 2.878841` i}, {5.5`,
> 1.357069`- 1.776964` i}, {6.5`,
> 1.259121`- 1.848249` i}, {8.5`,
> 1.105417`- 1.344566` i}, {9.5`,
> 1.119456`- 1.148945` i}, {11.5`,
> 1.082122`- 1.064767` i}, {14.5`,
> 1.015714`- 0.8684088` i}, {15.5`,
> 1.055329`- 0.664562` i}, {18.5`,
> 0.8675349`- 0.5107938` i}, {20.5`,
> 0.8968949`- 0.4148388` i}}
>
> FindFit[Data, Z, {R, G, H}, \[Omega]]
>
> FindFit::nrlnum: The function value {-0.658637+7.38957 \
> \[ImaginaryI],0.0321006+5.39846 \[ImaginaryI],-0.0241135+3.33901 \
> \[ImaginaryI],<<5>>,0.212762+0.769883 \[ImaginaryI],0.246899+0.605796
> \
> \[ImaginaryI],<<3>>} is not a list of real numbers with dimensions \
> {13} at {R,G,H} = {1.,1.,1.}. >>
>
> Why?!?!? Why can't FindFit handle this? What's wrong with it not
> being a list of real numbers? I'm pulling my hair out. I've looked
> at others' suggestions for similar problems and they don't work for
> this problem. Am I out of my mind? Does anyone have a suggeston?
>
> Regards,
>
> Benji
>