piecewise ranges [was Re: irreversibly reversing range]

[sfeam (E. Merritt) <eam...@gm...>]

On Monday, 10 September 2012, Tait <gnu...@t4...> wrote:
> > "sfeam (Ethan Merritt)" <sf...@us...>
> > >>> <aside>
> > >>> As you probably recall, my opinion is that a range specifier in the plot
> > >>> command is always a bad idea.  If it were just me, I'd remove that option
> > >>> altogether.  The only reason I can see to allow it is if it is changed so
> > >>> that the in-line range applies only to the immediately following plot clause.
> > >>> That way you could get separate ranges for separate plots:
> > >>>      plot [10:20] f1(x), [20:30] f2(x), [30:100] f3(x)
> > >>> I don't really like that either, but at least it would provide a
> > >>> capability that isn't addressed by simply doing "set xrange" first.
> > >>> </aside>
 
> I like the idea of separating axis range from (data/function) plot range.
> It's a somewhat frequently-asked question how to use a different range for
> a function than what is used for the axis, and the current solution -- to
> use a ternary -- isn't especially elegant.

I've put a patchset on SourceForge that implements this idea.
https://sourceforge.net/tracker/?func=detail&aid=3587664&group_id=2055&atid=302055

Its documentation says:

+ By default, computed functions or data generated for the pseudo-file "+" are
+ sampled over the entire range of the plot. This range may have been specified
+ by a prior `set xrange` command, by an explicit global range specifier at the
+ very start of the plot command, or by autoscaling of the range to span data
+ seen in all the elements of this plot command.  However, individual plot
+ elements can be assigned a more restricted sampling range.
+
+ Examples:
+
+ This establishes a total range on x running from 0 to 1000 and then plots
+ data from a file and two functions each spanning a portion of the total range:
+       plot [0:1000] 'datafile', [0:200] func1(x), [200:500] func2(x)
+
+ This is similar except that the total range is established by the contents
+ of the data file. In this case the sampled functions may or may not be
+ entirely contained in the plot:
+       set autoscale x
+       plot 'datafile', [0:200] func1(x), [200:500] func2(x)
+
+ This command is ambiguous. The initial range will be interpreted as applying to
+ the entire plot, not solely to the sampling of the first function as was
+ probably the intent:
+       plot [0:10] f(x), [10:20] g(x), [20:30] h(x)
+
+ This command removes the ambiguity of the previous example by inserting a dummy
+ definition so that the range is not the first element of the plot command:
+       plot dummy=0, [0:10] f(x), [10:20] g(x), [20:30] h(x)