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I want to fit experimental data by the H-N model. Here is the H-N model: $$\text{EHN}(T)\text{=}\text{E$\infty $}+\frac{\text{E0}-\text{E$\infty $}}{\left(1+\left(i \omega\tau(T_g)10^{-\frac{\text{C1} (T-\text{Tg})}{\text{C2}+(T-\text{Tg})}}\right)^{\alpha }\right)^{\beta }}$$

Here is my data and code.

 dataRe={{135., 2286.88}, {136., 1889.46}, {137., 1567.42}, {138., 1294.73}, {139., 1081.55}, {140., 902.773}, {141., 761.623}, {142., 643.534}, {143., 550.366}, {144., 470.925}, {145., 405.269}, {146., 348.847}, {147., 303.248}, {148., 263.789}, {149., 230.926}, {150., 202.368}, {151., 178.676}, {152., 158.557}, {153., 142.725}, {154., 129.218}, {155., 118.192}, {156., 108.735}, {157., 101.272}, {158., 94.8359}, {159., 89.3741}, {160., 84.4597}, {161., 80.1335}, {162., 76.1632}, {163., 72.6128}, {164., 69.2969}, {165., 66.227}, {166., 63.3502}, {167., 60.7664}, {168., 58.3432}, {169., 56.0645}, {170., 53.8886}, {171., 51.8571}, {172., 49.9009}, {173., 48.014}, {174., 46.1953}, {175., 44.4969}, {176., 42.8668}, {177., 41.3076}, {178., 39.7966}, {179., 38.3511}, {180., 36.9621}, {181., 35.6673}, {182., 34.4443}, {183., 33.3239}, {184., 32.2584}, {185., 31.245}, {186., 30.2813}, {187., 29.4031}, {188., 28.5708}, {189., 27.781}, {190., 27.0241}, {191., 26.3191}, {192., 25.6392}, {193., 24.975}, {194., 24.3329}, {195., 23.7381}, {196., 23.1738}, {197., 22.6451}, {198., 22.1308}, {199., 21.6239}, {200., 21.1439}, {201., 20.7245}, {202., 20.3002}, {203., 19.8216}, {204., 19.3485}, {205., 18.9218}, {206., 18.5166}, {207., 18.1276}, {208., 17.7492}, {209., 17.3845}, {210., 17.0318}, {211., 16.6938}, {212., 16.3641}, {213., 16.0424}, {214., 15.7233}, {215., 15.4063}, {216., 15.0967}, {217., 14.8008}, {218., 14.5269}, {219., 14.2817}, {220., 14.0376}, {221., 13.7849}, {222., 13.5334}, {223., 13.288}, {224., 13.0538}, {225., 12.831}, {226., 12.6145}, {227., 12.4025}, {228., 12.1932}, {229., 11.9889}, {230., 11.8003}, {231., 11.622}, {232., 11.442}, {233., 11.2606}, {234., 11.0808}, {235., 10.9046}, {236., 10.7371}, {237., 10.577}, {238., 10.4275}, {239., 10.2802}, {240., 10.1313}, {241., 9.98528}, {242., 9.84445}, {243., 9.70511}, {244., 9.56583}, {245., 9.42439}, {246., 9.28424}, {247., 9.16163}, {248., 9.05307}, {249., 8.94078}, {250., 8.82361}, {251., 8.70563}, {252., 8.58908}, {253., 8.47813}, {254., 8.37066}, {255., 8.26599}, {256., 8.16324}, {257., 8.06268}, {258., 7.9627}, {259., 7.86389}, {260., 7.77106}, {261., 7.68272}, {262., 7.59522}, {263., 7.50776}, {264., 7.4199}, {265., 7.33254}, {266., 7.24746}, {267., 7.16453}, {268., 7.0849}, {269., 7.00582}, {270., 6.92552}, {271., 6.84306}, {272., 6.76014}, {273., 6.68684}, {274., 6.62505}, {275., 6.56069}, {276., 6.4861}, {277., 6.4139}, {278., 6.34826}, {279., 6.28453}, {280., 6.2223}, {281., 6.16394}, {282., 6.10795}, {283., 6.04993}, {284., 5.99424}, {285., 5.94735}, {286., 5.90123}, {287., 5.84622}, {288., 5.78872}, {289., 5.74026}, {290., 5.69521}, {291., 5.65082}, {292., 5.60682}, {293., 5.56378}, {294., 5.52176}, {295., 5.48153}, {296., 5.44198}, {297., 5.40113}, {298., 5.36029}, {299., 5.32389}, {300., 5.29061}, {301., 5.25599}, {302., 5.22026}, {303., 5.18636}, {304., 5.15429}, {305., 5.12238}, {306., 5.09002}, {307., 5.05626}, {308., 5.0215}, {309., 4.9884}, {310., 4.95724}, {311., 4.9259}, {312., 4.89414}, {313., 4.86346}, {314., 4.83431}, {315., 4.80636}, {316., 4.77938}, {317., 4.75121}, {318., 4.72102}, {319., 4.69132}, {320., 4.66365}, {321., 4.63793}, {322., 4.61535}, {323., 4.5939}, {324., 4.57255}, {325., 4.55129}, {326., 4.53031}, {327., 4.50947}, {328., 4.48862}, {329., 4.46747}, {330., 4.44536}, {331., 4.42347}, {332., 4.40477}, {333., 4.3878}, {334., 4.36821}}; dataIm={{135., 887.339}, {136., 797.248}, {137., 701.968}, {138., 608.569}, {139., 523.492}, {140., 445.966}, {141., 379.817}, {142., 322.098}, {143., 274.838}, {144., 234.408}, {145., 201.682}, {146., 173.669}, {147., 150.826}, {148., 130.956}, {149., 114.338}, {150., 99.8744}, {151., 87.8489}, {152., 77.4709}, {153., 69.0043}, {154., 61.7297}, {155., 55.8849}, {156., 50.8427}, {157., 46.6994}, {158., 43.0493}, {159., 39.9282}, {160., 37.1165}, {161., 34.6505}, {162., 32.3913}, {163., 30.3725}, {164., 28.5008}, {165., 26.8072}, {166., 25.2321}, {167., 23.8052}, {168., 22.4737}, {169., 21.258}, {170., 20.1175}, {171., 19.0709}, {172., 18.0847}, {173., 17.1751}, {174., 16.3173}, {175., 15.5259}, {176., 14.7758}, {177., 14.076}, {178., 13.4098}, {179., 12.7869}, {180., 12.1926}, {181., 11.6359}, {182., 11.1054}, {183., 10.6106}, {184., 10.141}, {185., 9.7062}, {186., 9.29656}, {187., 8.922}, {188., 8.57166}, {189., 8.25434}, {190., 7.95882}, {191., 7.69154}, {192., 7.44172}, {193., 7.21152}, {194., 6.99187}, {195., 6.78149}, {196., 6.57857}, {197., 6.38792}, {198., 6.20788}, {199., 6.0449}, {200., 5.89388}, {201., 5.758}, {202., 5.62656}, {203., 5.49434}, {204., 5.36374}, {205., 5.23765}, {206., 5.11653}, {207., 5.00326}, {208., 4.89584}, {209., 4.79588}, {210., 4.70075}, {211., 4.61033}, {212., 4.52086}, {213., 4.43049}, {214., 4.33572}, {215., 4.23482}, {216., 4.13749}, {217., 4.04895}, {218., 3.96654}, {219., 3.89063}, {220., 3.81765}, {221., 3.74721}, {222., 3.67986}, {223., 3.61563}, {224., 3.55026}, {225., 3.48314}, {226., 3.41624}, {227., 3.34984}, {228., 3.28314}, {229., 3.2159}, {230., 3.14784}, {231., 3.08}, {232., 3.01543}, {233., 2.95542}, {234., 2.90456}, {235., 2.85808}, {236., 2.81372}, {237., 2.76943}, {238., 2.72368}, {239., 2.67735}, {240., 2.6309}, {241., 2.58498}, {242., 2.54007}, {243., 2.49639}, {244., 2.45405}, {245., 2.41249}, {246., 2.37127}, {247., 2.32927}, {248., 2.28662}, {249., 2.24441}, {250., 2.20277}, {251., 2.16184}, {252., 2.12168}, {253., 2.0829}, {254., 2.04515}, {255., 2.00862}, {256., 1.97252}, {257., 1.93656}, {258., 1.90105}, {259., 1.8665}, {260., 1.83418}, {261., 1.80359}, {262., 1.77372}, {263., 1.74444}, {264., 1.71617}, {265., 1.68854}, {266., 1.66149}, {267., 1.63461}, {268., 1.60756}, {269., 1.5805}, {270., 1.55363}, {271., 1.52752}, {272., 1.50251}, {273., 1.47878}, {274., 1.45619}, {275., 1.43259}, {276., 1.40649}, {277., 1.38075}, {278., 1.35628}, {279., 1.33193}, {280., 1.30753}, {281., 1.28371}, {282., 1.26006}, {283., 1.23519}, {284., 1.21085}, {285., 1.18961}, {286., 1.16996}, {287., 1.15244}, {288., 1.13717}, {289., 1.12452}, {290., 1.11253}, {291., 1.10009}, {292., 1.08708}, {293., 1.07289}, {294., 1.05803}, {295., 1.04329}, {296., 1.02881}, {297., 1.01485}, {298., 1.00133}, {299., 0.98825}, {300., 0.97555}, {301., 0.96326}, {302., 0.95127}, {303., 0.93939}, {304., 0.92759}, {305., 0.91595}, {306., 0.90446}, {307., 0.89313}, {308., 0.88195}, {309., 0.87097}, {310., 0.86024}, {311., 0.84998}, {312., 0.84021}, {313., 0.83063}, {314., 0.82119}, {315., 0.81193}, {316., 0.80287}, {317., 0.79377}, {318., 0.78453}, {319., 0.77542}, {320., 0.76659}, {321., 0.75783}, {322., 0.74902}, {323., 0.74036}, {324., 0.73211}, {325., 0.72417}, {326., 0.71666}, {327., 0.70927}, {328., 0.70162}, {329., 0.69383}, {330., 0.68607}, {331., 0.67845}, {332., 0.67127}, {333., 0.66448}, {334., 0.65796}}; EHN[T_] := E\[Infinity] + (E0 - E\[Infinity])/(1 + (I \[Omega] 10^(-((C1 (T - T0))/(C2 + (T - T0)))))^\[Alpha])^\[Beta]; fitRe=FindFit[dataRe,Re[EHN[T]],{{\[Alpha], 0.2}, {\[Beta], 0.6}, {E0, 4}, {E\[Infinity], 8000}, {C1, 17}, {C2, 50}, {\[Omega], 10}}, {T}}]; fitIm=FindFit[dataIm,Im[EHN[T]],{{\[Alpha], 0.2}, {\[Beta], 0.6}, {E0, 4}, {E\[Infinity], 8000}, {C1, 17}, {C2, 50}, {\[Omega], 10}}, {T}}]; Show[ListPlot[dataRe, PlotStyle -> Red], Plot[Re[EHN[T]] /. {fitRe}, {T, 1, 200}]] Show[ListPlot[dataIm, PlotStyle -> Orange], Plot[Im[EHN[T]] /. {fitIm}, {T, 1, 250}]]

However,I cannot fit the Real part and the Imaginary part well.Here is one of my fitted picture: enter image description here

Is there any method,which I can fit both the Re and Im part. Thanks.

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  • $\begingroup$ There are gaps in your code, brackets missing and there is no initial value for T0. $\endgroup$ Commented Jan 28, 2014 at 8:39
  • $\begingroup$ I'm so sorry. T0(or Tg) is 146 $\endgroup$ Commented Jan 28, 2014 at 9:04
  • $\begingroup$ Ok，thanks. I just find that Tg=146 maybe incorrect. $\endgroup$ Commented Jan 28, 2014 at 11:02

2 Answers 2

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data = {#, {#2, #4}} & @@@ Join[dataRe, dataIm, 2];

Ok, maybe I'm missing something but it seems there is no built in function to fit complex functions. So we have to create one:

model[T_, E∞_, E0_, ω_, C1_, T0_, C2_, α_, β_] := E∞ + (E0 - E∞)/(1 + (I ω 10^(-((C1 (T - T0))/(C2 + (T - T0)))))^α)^β; sol = FindMinimum[ Norm[Flatten[ ({Re[#], Im[#]} &[model[#, E∞, E0, ω, C1, T0, C2, α, β]] - #2) & @@@ data ]], {{α, 0.2}, {β, 0.6}, {E0, 4}, {E∞, 8000}, {C1, 17}, {C2, 50}, {ω, 10}, {T0, 110}}] 
{122.628, {α -> 0.303236, β -> 9.03512, E0 -> 10.3146, E∞ -> 7999.98, C1 -> 21.383, C2 -> 36.8504, ω -> 9.93816, T0 -> 121.931}} 
With[{opt = Sequence[PlotRange -> All, Axes -> False, Frame -> True, ImageSize -> 400, PlotStyle -> Thick, BaseStyle -> [email protected]]}, Row[{ Plot[Re@model[x, E∞, E0, ω, C1, T0, C2, α, β] /. sol[[2]], {x, 130, 335}, Epilog -> {Point[dataRe]}, opt, PlotLabel -> "Re part"], Plot[Im@model[x, E∞, E0, ω, C1, T0, C2, α, β] /. sol[[2]], {x, 130, 335}, Epilog -> {Point[dataIm]}, opt, PlotLabel -> "Im Part"] }]]

enter image description here

It is not perfect but this is the way. Try adjust initial values for example.

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  • $\begingroup$ I'm a freshman and I cannot read you code. I just copy the code and cannot get the result.Could you give me more details. $\endgroup$ Commented Jan 28, 2014 at 9:34
  • $\begingroup$ I got this:FindMinimum::nrnum: "函数值 [Sqrt](Abs[-887.339+Im[(7000. +Times[<<2>>])[135.,7000.,10.,10.,17.,120.,50.,0.3,9.]]]^2+Abs[-797.248+Im[(7000. +Times[<<2>>])[136.,7000.,10.,10.,17.,120.,50.,0.3,9.]]]^2+<<48>>+<<350>>) 不是位于 {[Alpha],[Beta],E0,E[Infinity],C1,C2,[Omega],T0} = {0.3,9.,10.,7000.,17.,50.,10.,120.} 的一个实数. " $\endgroup$ Commented Jan 28, 2014 at 10:09
  • $\begingroup$ @YuuhsingTuan Hello again, what the code does is calculating a vector: {Re@model(x_i), Im@model(x_i)}-data(x_i). Then we've got {{dRe1, dIm1}, {dRe2, dIm2}...}. Next Flatten and Norm produces: Sqrt[dRe1^2 + dIm1^2 + dRe^2 +...] and such expression is minimalzed with FindMinimum. It isn't the best, usually what is minimalized (LSQ) is D1^2 + D2^2..., you can modify. This shouldn't affect much. What can however, is changing initial values and/or model. It simply doesnt look like it can fit both now. You can also perform those procedures for model and data after taking double Log. $\endgroup$ Commented Jan 29, 2014 at 6:00
  • $\begingroup$ your second picture should be “point［dataIm］”.And then the result is very good.Thanks a lot. $\endgroup$ Commented Jan 29, 2014 at 6:06
  • $\begingroup$ @YuuhsingTuan Ha, right :D so it does fit :) Thanks. Nonetheless my comments are still valid for the future ;) Good luck. $\endgroup$ Commented Jan 29, 2014 at 6:11
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The model you are using in your code is missing a T0 which is shown in your question. I don't know why you would have arbitrarily dropped the parameter, but I have answered this question assuming that you know what you are doing. Using the approach described here you can model the Real and Imaginary parts simultaneously with using NonlinearModelfit:

model[T_, E∞_, E0_, ω_, C1_, T0_, C2_, α_, β_][part_] := Module[{f}, f = If[part == 1, Re, Im]; f[E∞ + (E0 - E∞)/(1 + (I ω 10^(-((C1 (T - T0))/(C2 + (T - T0)))))^α)^β]]; data = Join[ {#[[1]], 1, #[[2]]} & /@ dataRe, {#[[1]], 0, #[[2]]} & /@ dataIm]; nlm = NonlinearModelFit[data, model[T, E∞, E0, ω, C1, T0, C2, α, β][ part], {{α, 0.2}, {β, 0.6}, {E0, 4}, {E∞, 8000}, {C1, 17}, {C2, 50}, {ω, 10}, {T0, 110}}, {T, part}] nlm["BestFitParameters"] (* {α -> 0.325145, β -> 4.0862, E0 -> 7.3715, E∞ -> 6021.86, C1 -> 16.1477, C2 -> 26.291, ω -> 40.0271, T0 -> 125.429} *)

You do not get a terribly good fit with the initial parameters:

Plot[model[T, E∞, E0, ω, C1, T0, C2, α, β][1] /. nlm["BestFitParameters"], {T, 130, 335}, Epilog -> {Red, PointSize[0.01], Point /@ Take[data, Length[data]/2][[All, {1, 3}]]}] Plot[model[T, E∞, E0, ω, C1, T0, C2, α, β][2] /. nlm["BestFitParameters"], {T, 130, 335}, Epilog -> {Red, PointSize[0.01], Point /@ Drop[data, Length[data]/2][[All, {1, 3}]]}]

Mathematica graphics Mathematica graphics

Looking at the correlation matrix, we see that T0, ω, C1 and C2 are very strongly correlated, suggesting that you need to have very good initial estimates for these parameters, or better yet, you need to simplify your model.

nlm["CorrelationMatrix"] // MatrixForm

Mathematica graphics

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  • $\begingroup$ Thanks for your suggest about the model，but I could not change it.May be I can do something for the initials. $\endgroup$ Commented Jan 29, 2014 at 6:10
  • $\begingroup$ @YuuhsingTuan see my comment in Kuba's answer. The problem here is one of y-axis scale. $\endgroup$ Commented Jan 29, 2014 at 14:20
  • $\begingroup$ oa，I find it.Thanks a lot.But both of your results are better than mine.╯▂╰.And the Im/Re result is not fitted well.(๑´ω`๑) $\endgroup$ Commented Jan 29, 2014 at 14:29

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