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strange discrepancy between stats command result and fitting result

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  strange discrepancy between stats command result and fitting result "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2019-04-14 08:19 -0700
    Re: strange discrepancy between stats command result and fitting result Karl Ratzsch <mail.kfr@gmx.net> - 2019-04-14 18:56 +0200
      Re: strange discrepancy between stats command result and fitting result "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2019-04-14 23:46 -0700

#4180 — strange discrepancy between stats command result and fitting result

I am puzzled by the following discrepancy between a stats command result and the result which I have from normal Gnuplot fitting:

This is my Gnuplot batch-file
datafile='scallogmet.dat'
f(x)=a*log10(x)+b
a=-1.06
b=-4.78
fit [3e-3:1] f(x) datafile using ($1):($2) via a,b
stats [3e-3:1] datafile using (log10($1)):($2)

This is the content of scallogmet.dat:
0.001 -0.4421
0.002 -1.4743
0.003 -1.7844
0.004 -1.9640
0.005 -2.102
0.01 -2.483
0.02 -2.837
0.03 -3.034
0.04 -3.173
0.05 -3.28
0.1 -3.614
0.2 -3.96
0.3 -4.143
0.5 -4.408
1 -4.8
2 -5.294
3 -5.655
4 -5.96
5 -6.244
6 -6.509
7 -6.755
8 -7
9 -7.232
10 -7.46

The Gnuplot fitting gives me y=ax+b, with the correct a=-1.16816 and b=-4.78604
But the stats-command gives:  y = -3.104 x - 4.194
Why do U get the wrong result with stats?
thanks in advance

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#4181

Am 14.04.2019 um 17:19 schrieb hugocoolens@gmail.com:
> I am puzzled by the following discrepancy between a stats command result and the result which I have from normal Gnuplot fitting:

> f(x)=a*log10(x)+b
> a=-1.06
> b=-4.78
> fit [3e-3:1] f(x) datafile using ($1):($2) via a,b
> stats [3e-3:1] datafile using (log10($1)):($2)
> 
> 
> The Gnuplot fitting gives me y=ax+b, with the correct a=-1.16816 and b=-4.78604
> But the stats-command gives:  y = -3.104 x - 4.194


Not problem with fit or stats, your range setting for stats was
wrong: you have to logarithmise it as well

  stats [log10(3e-3):log10(1)] $dat using (log10($1)):($2)

and the linear model that comes out is y = -1.168 x - 4.786

;-)

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#4182

On Sunday, April 14, 2019 at 6:56:16 PM UTC+2, Karl Ratzsch wrote:
> Am 14.04.2019 um 17:19 schrieb hugocoolens@gmail.com:
> > I am puzzled by the following discrepancy between a stats command result and the result which I have from normal Gnuplot fitting:
> 
> > f(x)=a*log10(x)+b
> > a=-1.06
> > b=-4.78
> > fit [3e-3:1] f(x) datafile using ($1):($2) via a,b
> > stats [3e-3:1] datafile using (log10($1)):($2)
> > 
> > 
> > The Gnuplot fitting gives me y=ax+b, with the correct a=-1.16816 and b=-4.78604
> > But the stats-command gives:  y = -3.104 x - 4.194
> 
> 
> Not problem with fit or stats, your range setting for stats was
> wrong: you have to logarithmise it as well
> 
>   stats [log10(3e-3):log10(1)] $dat using (log10($1)):($2)
> 
> and the linear model that comes out is y = -1.168 x - 4.786
> 
> ;-)

Thanks a lot!
kind regards,
Hugo

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