Re: fit does not accept same range parameters as plot for time data

[sfeam <sf...@us...>]

On Sunday, 27 September 2015 08:50:54 AM pl...@pi... wrote:
> Hi
> 
> I have subset of a datafile that I can plot with plot command by 
> defining a range.
> The same range parameter is refused by fit:
> 
>      f(x)=a*exp(-(x-t0)/b)+c
>      format="%Y%m%d %H %M"
>      set timefmt format
>      set xdata time
>      plot ["20150925 02 33": "20150925 07 14"] "valana.txt"  u 1:4 w l
> 
>      a=b=c=t0=1;   fit f(x)  ["20150925 02 33": "20150925 07 14"] 
> "data.txt"  u 1:4 via a,b,c
> 
> 
> data looks like this:
> 
> 20150923 15 20 22.3 16.1
> 20150923 15 40 22.3 16.1
> 20150923 15 49 22.9 16.4
> 
> The fit command shows the following error:
> 
>    internal error: substring range specifiers must have integer values
> 
> 
> I thought the intention was that the two commands functioned in a 
> similar way. Why can't fit accept the range specifier in the same format 
> as plot?

This doesn't answer your question of why that particular command fails,
but ...

As always, I recommend never placing a range specifier inside the
plot (or fit) command.

Instead use:

   set xrange ["20150925 02 33": "20150925 07 14"]
   plot  "valana.txt"  u 1:4 w l
   a=b=c=t0=1;   
   fit f(x) "data.txt"  u 1:4 via a,b,c

Does that work better?

	Ethan