Groups > comp.graphics.apps.gnuplot > #312

Re: Wrong fit direction / zrange / unreadable graph file

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From	Ingo Thies <ingo.thies@gmx.de>
Newsgroups	comp.graphics.apps.gnuplot
Subject	Re: Wrong fit direction / zrange / unreadable graph file
Date	Mon, 16 May 2011 16:31:18 +0200
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On 16.05.2011 11:52, Christoph Bersch wrote:

> To reproduce the problem:
> 
> data.dat:
> 1 2.1
> 2 2.9
> 3 4.2
> 4 5.05
> 5 6
> 
> n = 0
> f(x) = m*x + n
> fit f(x) 'data.dat' via m,n

Strange. I see no reason for this since n is merely an additional offset
which could, depending on the function, even be negative. And the DNLS1E
routine from SLATEC doesn't have any problems here. How is fitting done
in gnuplot in particular?

BTW DNSL1E returns the following best-fit results, even with initial
n=m=0.0:

m = 0.995 +/- 0.041
n = 1.065 +/- 0.135

as does gnuplot with non-zero initial n. Maybe that routine has some
singular matrix trap which gnuplot doesn't have.

Ingo

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Thread

Wrong fit direction / zrange / unreadable graph file Katharina Miwege <k.miwege@googlemail.com> - 2011-05-15 23:59 -0700
  Re: Wrong fit direction / zrange / unreadable graph file Christoph Bersch <usenet@bersch.net> - 2011-05-16 11:04 +0200
    Re: Wrong fit direction / zrange / unreadable graph file Ingo Thies <ingo.thies@gmx.de> - 2011-05-16 11:34 +0200
      Re: Wrong fit direction / zrange / unreadable graph file Christoph Bersch <usenet@bersch.net> - 2011-05-16 11:52 +0200
        Re: Wrong fit direction / zrange / unreadable graph file Richard Owlett <rowlett@pcnetinc.com> - 2011-05-16 06:25 -0500
          Re: Wrong fit direction / zrange / unreadable graph file Christoph Bersch <usenet@bersch.net> - 2011-05-16 14:44 +0200
        Re: Wrong fit direction / zrange / unreadable graph file Ingo Thies <ingo.thies@gmx.de> - 2011-05-16 16:31 +0200
          Re: Wrong fit direction / zrange / unreadable graph file Katharina Miwege <k.miwege@googlemail.com> - 2011-05-16 09:01 -0700
            Re: Wrong fit direction / zrange / unreadable graph file Christoph Bersch <usenet@bersch.net> - 2011-05-17 08:46 +0200
              Re: Wrong fit direction / zrange / unreadable graph file Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-05-19 01:34 +0200
          Re: Wrong fit direction / zrange / unreadable graph file Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-05-19 01:49 +0200
            Re: Wrong fit direction / zrange / unreadable graph file Ingo Thies <ingo.thies@gmx.de> - 2011-05-19 11:07 +0200
              Re: Wrong fit direction / zrange / unreadable graph file Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-05-19 14:02 +0200
      Re: Wrong fit direction / zrange / unreadable graph file Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-05-19 01:39 +0200
        Re: Wrong fit direction / zrange / unreadable graph file Ingo Thies <ingo.thies@gmx.de> - 2011-05-19 10:58 +0200

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