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Re: Fit data with range

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88402] Re: Fit data with range
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 5 May 2008 06:08:19 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fvhdv7$3q6$1@smc.vnet.net>

Ivan wrote:

> I want to fit a polynomial function to a set of data,
> only between say xmin to xmax. How can I do that?
> I know only how to fit the whole range.
> 
> For example:
> 
> data = ReadList["file.dat",{Number,Number}];
> 
> fit = Fit[data,{1,x,x^2},x]
> 
> Plot[fit,{x,0,10}]

You could use *Select[]* to massage your data. For instance,

data = {{0, 1}, {1, 0}, {3, 2}, {5, 4}, {7, 8}, {9, 11}};
xmin = 1; xmax = 7;
pts = Select[data, xmin <= #[[1]] <= xmax &]
fit = Fit[pts, {1, x, x^2}, x]
Show[ListPlot[pts, PlotStyle -> {Red, PointSize -> Large}],
  Plot[fit, {x, xmin, xmax}, PlotStyle -> {Blue, Thick}]]

{{1, 0}, {3, 2}, {5, 4}, {7, 8}}


                         2
-0.325 + 0.3 x + 0.125 x

Regards,
-- Jean-Marc


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