Re: fit ignores yrange

[<pl...@pi...>]

On 05/06/15 22:49, Ethan A Merritt wrote:
> On Friday, 05 June, 2015 16:36:12 Karl Ratzsch wrote:
>> Hi,
>>
>> as Ethan has started preparing the release of 5.0pl1, I wanted to draw
>> attention to this bug
>>
>> https://sourceforge.net/p/gnuplot/bugs/1594/
>>
>> . Since gp5.0, "fit" ignores any set y range, both from "set yrange" or
>> inline.
>
> As I understand it, all fits now use "z" as the function range variable.
> So in order to restrict the function range, use
>
>    set zrange [min:max]
>
> I don't know what the intent was with regard to adding in-line
> range restrictions in the "fit" command.
>
> 	Ethan
>
>
>
>
>> It's a rather bad regression against previous versions, and one that's
>> possibly hard to spot for some people. It'd be great if the next release
>> contained a fix.
>>
>> Many thanks in advance, and of course to all developers!
>>
>> Best regards
>>
>>     Karl
>>
>>

setting xrange, either explicitly or via a range parameter to fit 
command, works as expected.

  m=c=0.1;fit [1975:2000] lin(x) datafile u 1:2 via m,c;

since x is by convention the independent variable and is REQUIRED to 
have negligible  error  and negligible non linear variability to 
regression to give an accurate estimation of the supposed linear 
relationship, this seems appropriate.

I don't understand where z comes into the discussion in x,y data. :?

Trying to set the range of the fitting process by defining a range on 
the dependent variable suggests it may be being applied correctly. I can 
understand that the algorithm doing the fitting is based on the 
assumption that x is the independent variable and that is it xrange that 
defines any subset used for a particular fit.

Maybe this needs to be stated explicitly in the documentation.

Peter.