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Re: findfit or solve?

• To: mathgroup at smc.vnet.net
• Subject: [mg55035] Re: [mg55013] findfit or solve?
• From: DrBob <drbob at bigfoot.com>
• Date: Thu, 10 Mar 2005 05:24:42 -0500 (EST)
• References: <200503091134.GAA07043@smc.vnet.net>
• Reply-to: drbob at bigfoot.com
• Sender: owner-wri-mathgroup at wolfram.com

It helps to write the model in Mathematica notation.

data = {{6.968, 117.1}, {7.967, 123.3}, {9.046, 129.4},
     {9.982, 134.6}, {10.951, 139.2}, {11.973, 145.2},
     {13.021, 151.1}, {13.892, 159.9}, {14.888, 167.8},
     {15.858, 171.9}, {16.857, 175.7}, {17.854, 177.2},
     {18.724, 175.6}};
constants = {a -> 176, b -> 160, c -> 0.1, d -> 14, e -> 1.2};
model = h1 - (2*(h1 - hθ))/(Exp[s0*(t - θ)] + Exp[s1*(t - θ)]);
f = model /. constants;
params = Complement[
     Union[Cases[f, (x_Symbol)?
        ( !NumericQ[#1] & ),
       Infinity]], {t}];
NonlinearFit[data, f, {t}, params]

151.3846153846154 -
   111410.8547029138/
    (E^(-14.335393999263037*
       (-115.43433836614763 +
        t)) +
     E^(-14.335393999252005*
       (-115.43433836614763 + t)))

Bobby

On Wed, 9 Mar 2005 06:34:39 -0500 (EST), Tegla Bela <spiller at hotmail.co.jp> wrote:

> Greetings to everybody,
>
> I have found a model and I would like to use Mathematica for the data under
> the model. The model is as follows:
>
> = h1 - ((2 * (h1 - hθ)) / ((EXP(s0 * (t -θ))) + (EXP(s1 * (t -θ)))))
>
> data = {{6.968, 117.1}, {7.967, 123.3}, {9.046,
>       129.4}, {9.982, 134.6}, {10.951,
>        139.2}, {11.973, 145.2}, {13.021, 151.1}, {13.892, 159.9}, {
>       14.888, 167.8}, {15.858, 171.9}, {16.857, 175.7}, {17.854, 177.2}, {
>       18.724, 175.6}};
>
> I have managed to do it with nonlinear least-square fitting in other
> program. But not working for me in Mathematica. (I do not know how to give
> initial values to have the five unknown parameters estimated) These are the
> initial values that I would like to use: a=176, b=160, c=0.1, d=14, e=1.2
> (t is the age, first value in each pair of the data)
>
> Does anybody have idea how it can be done? Any help is appreciated.
>
> Spiller
>
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>



-- 
DrBob at bigfoot.com

• References:
  • findfit or solve?
    • From: "Tegla Bela" <spiller@hotmail.co.jp>