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Re: Impedance Equation fit to Complex Data

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86550] Re: Impedance Equation fit to Complex Data
  • From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
  • Date: Thu, 13 Mar 2008 04:35:41 -0500 (EST)
  • Organization: University System of Maryland
  • References: <fr7opm$39a$1@smc.vnet.net> <fr8b6s$h0d$1@smc.vnet.net>

I don't believe that this is true. I use FindFit often to find the 
coefficients of Exp[+I k x] and Exp[-I k x] for Quantum Mechanical 
boundary reflections. Something else is going on here.

Kevin

Jens-Peer Kuska wrote:
> Hi,
> 
> FindFit[] cant handle complex values ? as the error message
> 
> "The function value {-0.658637+7.38957\ I,0.0321006+5.39846\ \
> I,<<8>>,<<3>>} is not a list of real number"
> 
> say ?
> 
> Regards
>    Jens
> 
> 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
>>
> 

-- 

Kevin J. McCann
Research Associate Professor
JCET/Physics
Physics Building
University of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250


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