Re: interpretation of fit errors

[Ethan A M. <sf...@us...>]

On Thursday, May 05, 2011 12:01:53 am Bastian Märkisch wrote:
> > I may be missing something, but why not just report both
> > absolute and relative errors?   The user is free to pick whichever
> > is relevant to the particular case at hand.   No extra options needed.
> >
> >       Ethan
> 
> I think you just proved that the name may be misleading ;). This is 
> about the interpretation of data errors (input), and the resulting 
> scaling with FIT_STDFIT of reported variable errors (output). This is 
> not about reporting relative errors as in a_err/a.

From Thomas Mattison's mail that you linked to
   http://thread.gmane.org/gmane.comp.graphics.gnuplot.devel/3737/focus=3740

  Gnuplot already does the right calculation internally, it just doesn't
  report it.  It reports only a non-standard,  fluctuation-sensitive error
  (although I will grant that it is possible  in most cases to recover the
  standard error from the fit log by some simple hand calculations).

I took this to mean that the issue is ultimately one of reporting.
Right now we report errors calculated under one set of assumption;
he is asking that we also report errors calculated under a different
set of assumption.  My question is why not just report both?
The current values become a set of "FIT_*_SCALED_*" output parameters
and the new ones become a parallel set of "FIT_*_UNSCALED_*" parameters.

But I admit to saying this without having thought deeply about the
underlying issue.  Just ignore me if I'm not making sense :-)

> Not only is scaling the errors wrong in certain cases, but these error 
> values are also saved to variables for further processing, e.g. in 
> labels. Since, the user should be able to select. With `set fit abs` 
> gnuplot reports the same errors as e.g. CERN Minuit.
> 
> Any other ideas about the names? weights|errors? scaling|noscaling? 
> weights|real?
> 
>    Bastian
>