Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.graphics.apps.gnuplot > #4169

Re: different behaviour gnuplot4 and 5 concerning "Implied independent variable y not found in fit function"

Show key headers only | View raw

Am 21.03.2019 um 16:02 schrieb hugocoolens@gmail.com:
> In a batch-file which worked fine for Gnuplot 4, I had the following lines:
> f(x) = a*10e-8*(exp(x/b)-1)
> err1(y)=0.01*0.033*y+2e-9
> err2(y)=0.01*0.0031*y+20e-9
> err3(y)=0.01*0.0034*y+200e-9
> err4(y)=0.01*0.0045*y+2e-6
> error(y)=(y<10e-6)? err1(y):(y<100e-6)? err2(y):(y<1e-3)? err3(y):err4(y)
> a=30e-3
> b=50e-3
> fit f(x) '1n4148_linstep_1na_10ma.dat' using ($1):($2):(error($2)) via a,b
> 
> This worked fine in Gnuplot 4, however when I try this in Gnuplot 5, I get the following error message:
> 	> Implied independent variable y not found in fit function.
> 	> Assuming version 4 syntax with zerror in column 3 but no zerror keyword.
> 

It's only a warning, not an error. Doesn't the fit converge?

I tried this:

   set xr [0:1e-3]
   fit f(x) '+' using ($1):(f($1)):(error(f($1))) via a,b

where gp of course can't compute errors from the perfect data, but
otherwise works fine.

To get rid of the warning, you specify to which variable the
additional error column refers:

      fit f(x) '1n4148_linstep_1na_10ma.dat' using
($1):($2):(error($2)) yerror via a,b

(you can also give "zerror" or "error z", that's all the same if you
only have one dependent and one independent variable.)

I understand the warning to be just one warning, not two: You gave
three columns, but the fit function only has one variable. That
makes gnuplot assume (correctly,) that you don't have two
independent variables, but one, plus an additional column with
y(==z)-errors.


   Best, Karl

Back to comp.graphics.apps.gnuplot | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

different behaviour gnuplot4 and 5 concerning  "Implied independent variable y not found in fit function" "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2019-03-21 08:02 -0700
  Re: different behaviour gnuplot4 and 5 concerning "Implied independent variable y not found in fit function" Karl Ratzsch <mail.kfr@gmx.net> - 2019-03-21 22:02 +0100
    Re: different behaviour gnuplot4 and 5 concerning "Implied independent variable y not found in fit function" "hugocoolens@gmail.com" <hugocoolens@gmail.com> - 2019-03-22 01:14 -0700

csiph-web