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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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dinodeblasio@gmail.com

Posts: 23
Registered: 10/14/07
Re: Help: Problems with fitting a list of data with an equation with
Posted: Feb 8, 2013 5:10 AM
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Hello Robert,

thanks for the help, however still I have some error coming from my fitting, I tried:
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][[1]] // FullSimplify,
param = FindFit[data1211, y[t] /. model, {A, B}, t],
Plot[y[t] /. model /. param, {t, 0, Max[data1211[[All, 1]]]},
PlotRange -> All, ImageSize -> 350, PlotStyle -> {Black},
AxesLabel -> {"", "Ca,mol/liter"}, BaseStyle -> {FontSize -> 15},
Epilog -> {Text["Step [1]", {50, 0.00002}],
Text["(sec)", {140, 0.00002}], Point[data1211]}]}] // Quiet

and gave me some errors.

what it could be?
Thanks again,

Dino


Il giorno gioved=EC 7 febbraio 2013 04:27:39 UTC+2, roby ha scritto:
> 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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