Re: irreversibly reversing range

[Daniel J S. <dan...@ie...>]

On 09/10/2012 05:34 PM, Ethan A Merritt wrote:
> On Monday, September 10, 2012 01:16:41 pm Daniel J Sebald wrote:

>>> <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>
>>
>> Yes, I sort of agree with that.  That is why I picked the phrasing that
>> the range is associated with the data, not the orientation of the axis.
>>    Given the example you wrote, the paradigm is that [10:20] means the
>> data for which x is between 10 and 20, and in that case [20:10] is no
>> different than [10:20].  Using the range specifier to control the
>> orientation of the plot in your example would be a mess.
>
> The way I view it is that   "set xrange [FOO:BAZ]" means the left
> end of the axis is pinned at FOO and the right end is pinned at BAZ.
> The makes sense both externally (what the user sees) and internally
> (mapping a numerical coordinate onto a screen position).
>
> I will note that my primary motivation for the change in 4.7 was to clean
> up the code internally.  The fact that it also IMHO makes a more sensible
> user-visible syntax is just a side benefit.  The change removed a
> tangle of calls and macros like check_axis_reversed(), CHECK_REVERSE,
> AXIS_ACTUAL_MIN, etc, and made it a lot easier to implement linked
> primary/secondary axes.  It also fixed corruption in the zoom/restore
> state if the AXIS_REVERSE flag somehow got set while a plot was zoomed.

That's good.  There's a natural complexity to these sorts of things and 
controlling the range doesn't seem like it should be so complex.


>> Anyway, the most affect on backward compatibility is
>> ["reverse" only applies to the autoadjust settings]
>> so I'm wondering why that change is preferred.
>
> The `reverse` keyword was added sometime between versions 3.5 and 3.7
> Its documentation has always said
>    `reverse` is intended primarily for use with `autoscale`

Oh, then that was a bug when released.  The "NB: This is a change 
introduced in version 4.7." comment in the xrange documentation suggests 
the old behavior was intentional.  I have the fix for Octave ready to go 
then.


> Dan, you are again showing tests with function plots.
> I keep pointing out that the x-axis autoscaling commands, including the
> * character in a "set xrange" command _do not apply_ to the samples generated
> for functions.   I am pretty sure that whatever result you get is pure
> happenstance; it was not a deliberate design decision, and the use of * for
> function domains was never documented because its use was not intended.

I included the function x so that it illustrates the data points passing 
through the line and that things are working properly.  Try without the 
function x and it is the same result.  I'll do this with a bit more 
detail, and I will use 9 as a lower limit so as to rule out some strange 
conflict between the [-10:10] of the default range:

	G N U P L O T
	Version 4.7 patchlevel 0    last modified 2012-06-19
	Build System: Linux x86_64

	Copyright (C) 1986-1993, 1998, 2004, 2007-2012
	Thomas Williams, Colin Kelley and many others

	gnuplot home:     http://www.gnuplot.info
	mailing list:     gnu...@li...
	faq, bugs, etc:   type "help FAQ"
	immediate help:   type "help"  (plot window: hit 'h')

Terminal type set to 'qt'
gnuplot> show xrange

	set xrange [ * : * ] noreverse nowriteback  # (currently 
[-10.0000:10.0000] )

gnuplot> set xrange [9:*]
gnuplot> show xrange

	set xrange [ 9.00000 : * ] noreverse nowriteback  # (currently [:10.0000] )

gnuplot> plot '-'
input data ('e' ends) > 5 5
input data ('e' ends) > 8 8
input data ('e' ends) > 12 12
input data ('e' ends) > 15 15
input data ('e' ends) > e
gnuplot> show xrange

	set xrange [ 9.00000 : * ] noreverse nowriteback  # (currently [:15.0000] )


My plot is showing the xaxis starting at 9 and ending at 15.  Shouldn't 
that be saying "currently [9.0000:15.0000]", because that is currently 
what the range is on the plot?

Dan