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Re: Help with fitting


data = {{0.1, 1400}, {0.5, 10}, {1, 5}, {5, 20}, {10, 250}};


I am guessing that this is what you intended for the equation


eqn = Log [y/b] == Log [a*x/b + a*x/b] + (-0.22 + Log [a*x/b]^2) //
   Rationalize;


expr = (y /. Solve[eqn, y][[1]])[[1]];


param = FindFit[data, expr, {a, b}, x]


{a -> 1.14522, b -> 2.27658}


LogLogPlot[
 Evaluate[expr /. param],
 {x, .05, 20},
 Epilog -> {Red,
   AbsolutePointSize[4],
   Point[Log[data]]}]



Bob Hanlon


On Fri, Aug 9, 2013 at 1:48 AM, ismail <ism45 at yahoo.com> wrote:

> Hello,
>
> I have experimental data with (y) and (x)
>
> I need to fit them into the following model
>
> Log (y/b) = Log (ax /b/1+ax/b) + (-0.22/1+(log ax/b)^2)
>
> The result should be a plot with Log y on the y-axis, Log x in the x axis.
> and the two constants a and b will be the result of the fitting.
>
> I tried that in Mathematica, but my problem is that I don't know how to
> define the function so I can keep (Logy/b) in the left side.
>
> Mathematica allows me only to defin a model in the form (y=f(x))
>
> Any help please?
>
>


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