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Groups > comp.graphics.apps.gnuplot > #1031

Re: two regression curves for two ranges of the same data set on the same chart

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On 12.04.2012 22:50, TonyG wrote:
> I've been trying to obtain two sets of regression coefficients for the
> same data file, using two ranges of x values, then plot the two lines
> and the data points on the same graph.
>
> f(x)=a*x+b
> f(x1)=a1*+b1,  then

That one almost certainly doesn't do what you wanted.  There's no x1 on 
the right hand side, and you just overwrote your earlier definition of 
f(x).  You must have meant

	f1(x) = a1*x+b1

> fit [x=*:25] f(x)... via a, b  and
> fit [x1=25:*] f(x1) ... via a1, b1

	f(x) = (x<=25) ? (a*x+b) : (a1*x+b1)
	fit f(x) via a, b, a1, b1

would have been simpler.

> The trouble is with the x1... gnuplot doesn't understand what it is.

I'd have to state that you don't understand it either...

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two regression curves for two ranges of the same data set on the same chart TonyG <tgozdz@gmail.com> - 2012-04-12 13:50 -0700
  Re: two regression curves for two ranges of the same data set on the same chart Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-04-13 00:42 +0200
    Re: two regression curves for two ranges of the same data set on the same chart TonyG <tgozdz@gmail.com> - 2012-04-13 05:23 -0700
      Re: two regression curves for two ranges of the same data set on the   same chart Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-04-13 20:37 +0200

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