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MathGroup Archive 2000

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How to use BestFitParameters?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24274] How to use BestFitParameters?
  • From: piovere at pdq.net (rob)
  • Date: Wed, 5 Jul 2000 23:10:59 -0400 (EDT)
  • Organization: PDQ.net (using Airnews.net!)
  • Sender: owner-wri-mathgroup at wolfram.com

p is a list of data pairs { {x1,y1}, {x2,y2}, ....} and when I fit
this data to a function Mathematica does a pretty good job of doing the fit:

NonlinearRegress[p, a/Sqrt[d^2 + (x1 - w0)^2], {x1}, {a, d, w0}, 
  MaxIterations -> 200, RegressionReport -> BestFitParameters]

gives this as an output:
{BestFitParameters -> {a -> 1.07061, d -> 0.300272, w0 -> 28.8068}}

I know it is pretty a pretty good fit to the data because I can use
another program like Excel to plot the curve using these parameters
and display it next to the data.  It sure would be nice to do this in
Mathematica without going to an outside program.  I've tried things but I
can't seem to be able to get to the parameters a, d and w0.  I can't
even list them.  For example,  I'd like to display the number
d/Sqrt[w0^2-d^2]. So I tried this:

d/Sqrt[w0^2-d^2] /. %

All I get is the formula in symbolic form.

Can someone here provide some relief?

Thanks, Rob




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