Groups > comp.graphics.apps.gnuplot > #3669

Re: What's new in gnuplot 5.2

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Subject	Re: What's new in gnuplot 5.2
From	"hugocoolens@gmail.com" <hugocoolens@gmail.com>
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Op zaterdag 3 juni 2017 22:45:42 UTC+2 schreef Hans-Bernhard Bröker:
> Am 03.06.2017 um 21:49 schrieb hugocoolens@gmail.com:
> 
> 
> >> Just out of curiosity, what is the function you try to fit?
> > this is one example:
> > f(x)=20*log10(a/(1+(x/b)**2)**0.5)
> > a should be positive but sometimes Gnuplot makes it negative
> 
> Often the function can be transformed a bit to lift such requirements. 
> In this case, you could just fit
> 
> 	f(x) = 10 * log10(a**2 / (1 + (x / b)**2))
> 
> or
> 
> 	f(x) = 20 * log10a - 10 * log10(1 + (x / b)**2)
thank you very much for your help, I tried out 
f(x) = 20 * log10a - 10 * log10(1 + (x / b)**2) but that didn't make 
any difference. However f(x) = 10 * log10(a**2 / (1 + (x / b)**2)) does make a difference but "a" still becomes negative for certain fitting intervals.
I have posted the data here:
https://www.dropbox.com/s/slhg33xoep51i02/karakt.dat?dl=1
And this is the batch-file I used:
https://www.dropbox.com/s/crkpcbvd9a1qq4r/amplitude.gp?dl=1
You will see the sign of "a" toggles to negative when the fitting interval is greater than 80e6 even though the fitting as such seems very good.

kind regards,
Hugo

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What's new in gnuplot 5.2 Raoul Fleckman <raoul.fleckman@gmail.com> - 2017-05-26 21:13 +0000
  Re: What's new in gnuplot 5.2 "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2017-05-31 23:16 -0700
    Re: What's new in gnuplot 5.2 Karl Ratzsch <mail.kfr@gmx.net> - 2017-06-02 10:18 +0200
      Re: What's new in gnuplot 5.2 "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2017-06-02 02:32 -0700
        Re: What's new in gnuplot 5.2 Karl Ratzsch <mail.kfr@gmx.net> - 2017-06-02 12:11 +0200
          Re: What's new in gnuplot 5.2 "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2017-06-03 12:49 -0700
            Re: What's new in gnuplot 5.2 Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-06-03 22:45 +0200
              Re: What's new in gnuplot 5.2 "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2017-06-05 01:32 -0700
                Re: What's new in gnuplot 5.2 Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-06-05 14:47 +0200
                Re: What's new in gnuplot 5.2 "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2017-06-06 23:34 -0700
                Re: What's new in gnuplot 5.2 Dr Engelbert Buxbaum <engelbert_buxbaum@hotmail.com> - 2017-06-07 14:26 +0200

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