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