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Groups > comp.graphics.apps.gnuplot > #3674

Re: What's new in gnuplot 5.2

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Op maandag 5 juni 2017 14:47:38 UTC+2 schreef Hans-Bernhard Bröker:
> Am 05.06.2017 um 10:32 schrieb hugocoolens@gmail.com:
> > Op zaterdag 3 juni 2017 22:45:42 UTC+2 schreef Hans-Bernhard Bröker:
> 
> >> 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.
> 
> Part of the trick is that this doesn't actually matter.  The function is 
> identical for parameters a and -a, so you can just throw away the sign 
> afterwards.  The requirement that a be positive was an artificial one 
> from the beginning.

I admit this wasn't a good example to make my point. However I still wonder why increasing the fitting interval toggles  the value of "a" from positive to negative.

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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