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Topic: Help: Problems with fitting a list of data with an equation with two parameters
Replies: 3   Last Post: Feb 12, 2013 3:23 AM

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roby.nowak@gmail.com

Posts: 86
Registered: 5/8/07
Re: Help: Problems with fitting a list of data with an equation with
Posted: Feb 6, 2013 9:27 PM
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Hi Dino,

As a first hint:

model = Solve[-A/(2 Sqrt[
B^2 + 4 A B]) (Log[(2 A y^2 + b -
Sqrt[B^2 + 4 A B])/(2 A y^2 + b + Sqrt[B^2 + 4 A B])]) -
A/(2 Sqrt[
B^2 + 4 A B]) (Log[(b - Sqrt[B^2 + 4 A B])/(b +
Sqrt[B^2 + 4 A B])]) == t, y][[1]] // FullSimplify



you can't youse {} as instead of () for groupung of expressions.

{} in Mathematica is used for arrays.


Further you must ensure that you choose a realvalued modell (not complex) before trying to fit.

Regards Robert


Am Mittwoch, 6. Februar 2013 07:50:43 UTC+1 schrieb dinode...@gmail.com:
> Hello everyone:
>
> I'd like to fit a list like:
>
> data2211={{0., 0.}, {1., 0.0000202672}, {2., 0.0000606506}, {3.,
>
> 0.0000902571}, {4., 0.00011201}, {5., 0.000122325}, {6.,
>
> 0.000129026}, {7., 0.000136861}, {8., 0.000138904}, {9.,
>
> 0.000142179}, {10., 0.000145617}, {11., 0.000150792}, {12.,
>
> 0.000153723}, {13., 0.000158662}, {14., 0.000163744}, {15.,
>
> 0.000170338}, {16., 0.000176373}, {17., 0.000184436}, {18.,
>
> 0.000191055}, {19., 0.000197175}, {20., 0.000205177}, {21.,
>
> 0.000212824}, {22., 0.000221142}, {23., 0.000228844}, {24.,
>
> 0.000236553}, {25., 0.000243398}, {26., 0.000251118}, {27.,
>
> 0.000258642}, {28., 0.00026638}, {29., 0.000275992}, {30.,
>
> 0.000284433}, {31., 0.000291682}, {32., 0.000300548}, {33.,
>
> 0.000308275}, {34., 0.000316503}, {35., 0.000322813}, {36.,
>
> 0.000332034}, {37., 0.000340994}, {38., 0.000349994}, {39.,
>
> 0.00035922}, {40., 0.000366491}, {41., 0.00037264}, {42.,
>
> 0.000379767}, {43., 0.000388169}, {44., 0.000395309}, {45.,
>
> 0.000403434}, {46., 0.000411034}, {47., 0.00041769}, {48.,
>
> 0.000424886}, {49., 0.000431168}, {50., 0.000437785}, {51.,
>
> 0.000446171}, {52., 0.000453136}, {53., 0.000460042}, {54.,
>
> 0.000467164}, {55., 0.000473857}, {56., 0.00047967}, {57.,
>
> 0.00048695}, {58., 0.000492749}, {59., 0.000499251}, {60.,
>
> 0.000506003}, {61., 0.000512512}, {62., 0.000516679}, {63.,
>
> 0.000522183}};
>
>
>
> with something like:
>
> Clear[y];
>
> Column[{model =
>
> Solve[-A/(
>
> 2 Sqrt[B^2 + 4 A B]) {Log[(2 A y^2 + b - Sqrt[B^2 + 4 A B])/(
>
> 2 A y^2 + b + Sqrt[B^2 + 4 A B])]} - -A/(
>
> 2 Sqrt[B^2 + 4 A B]) {Log[(b - Sqrt[B^2 + 4 A B])/(
>
> b + Sqrt[B^2 + 4 A B])]} == t, y[t], t][[1]],
>
> param = FindFit[data1211, y[t] /. model, {A, B}, t],
>
> Plot[y[t] /. model /. param, {t, 0, Max[data1211[[All, 1]]]},
>
> PlotRange -> All}]}] // Quiet
>
>
>
> however there is some errors which I can't figure it out.
>
> Any help is appreciated.
>
>
>
> Thanks,
>
> Dino






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