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MathGroup Archive 2005

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Re: FinFit question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54834] Re: [mg54816] FinFit question
  • From: DrBob <drbob at bigfoot.com>
  • Date: Fri, 4 Mar 2005 05:07:33 -0500 (EST)
  • References: <200503030329.WAA21066@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Do it this way:

<< Statistics`NonlinearFit`
points = {{23400, 273.2}, {6800, 298.2}, {2400, 323.2}};
T[R_] = NonlinearFit[points, B/(Log[R] - logRo), {R}, {B, logRo}]
T /@ points[[All, 1]]

4021.0588923624114/
   (4.658619219272381 + Log[R])

{273.186, 298.225, 323.188}

The original form (using Ro) is asking for trouble because you have (in your mind alone) an assumption that Ro>0. There is no such restriction on logRo.

Bobby

On Wed, 2 Mar 2005 22:29:06 -0500 (EST), Zsolt Regály <zs.regaly at icsip.elte.hu> wrote:

> Hi
>
> I have used Mathematica 4.2 to solve this problem
>
>     points = {{23400, 273.2}, {6800, 298.2}, {2400, 323.2}};
>     T[R_] = NonlinearFit[points, B/Log[R/Ro], {R}, {B, Ro}];
>
> wihich gives the result as
>
>     4021.05/Log[105.49 R]
>
>
> That is a good result, but when I try to do the same in Mathematica 5.0
> I get error messaeges and an other solutions, which is surely bad
>    1556.90/Log[-0.014 R]
>
> Why doesn't work FindFit for this function in Mathematica 5.0
>
> Regards,
> Zsolt Regaly (zs.regaly at astro.elte.hu)
>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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