       Re: findfit or solve?

• To: mathgroup at smc.vnet.net
• Subject: [mg55026] Re: findfit or solve?
• Date: Thu, 10 Mar 2005 05:24:25 -0500 (EST)
• References: <d0modp\$76l\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```For this to work in Mathematica you need to fix some syntax problems
and load a special package, Statistic`NonlinearFit`.  Be careful, the
symbol enclosing the Nonlinear fit is not a single quote or apostrophe
but a backwards single quote.  On my keyboard it is the shifted key to
the left of the "1" key.  I have shown the two differenct versions:
NonlinearFit just returns the best fit function.  NonlinearRegress

In my example below I load the graphics package Graphics`Colors` so
that I can access the color names in the final plot (See the Help under
Colors).  I also load Graphics`Graphics` so that I can use the
DisplayTogether command for showing multiple plot.

The code is at the end

In:=
<< Statistics`NonlinearFit`

In:=
<<Graphics`Graphics`
<<Graphics`Colors`

In:=
func = a - 2*(a-b)/(Exp[c*(t-d)]+Exp[e*(t-d)])

In:=
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}};

In:=
fitfunc =
NonlinearFit[data,func,t,{{a,176},{b,160},{c,0.1},{d,14},{e,1.2}}]

In:=
NonlinearRegress[data,func,t,{{a,176},{b,160},{c,0.1},{d,14},{e,1.2}}]

In:=
DisplayTogether[
ListPlot[data],
Plot[func/.{a->176,b->160,c->0.1,d->14,e->1.2},{t,7,20},
PlotStyle\[Rule]{Blue}],
Plot[fitfunc,{t,7,20},PlotStyle\[Rule]{Red}]]

Tegla Bela 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 - h\$B&H(B)) / ((EXP(s0 * (t -\$B&H(B))) + (EXP(s1 * (t
-\$B&H(B)))))
>
> 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
>
> _________________________________________________________________
> \$BF|K\9qFb:GBg5i(B570\$BK|%f!<%6!<\$N(BMSN Hotmail
> https://registernet.passport.net/reg.srf?id=2&lc=1041

```

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