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Groups > comp.graphics.apps.gnuplot > #2346

Re: Major and minor ticks artifact

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Janis Papanagnou wrote:

> On 02.03.2014 20:10, Hans-Bernhard Bröker wrote:
>> On 02.03.2014 18:19, Janis Papanagnou wrote:
>>> I noticed an ugly artifact that at on place a minor tic is
>>> unnecessarily displayed, and even straight *besides* the major tic.
>>> This was with a png
>>> term definition  set term png size 800,600 . If I change that
>>> definition
>>> to  set term png size 800,599  the artifact disappears. It's, yet
>>> again, a work-around.
>>>
>>> Is that how gnuplot works and how experienced people "solve" such
>>> issues, or is there any better approach?
>> 
>> How is anyone supposed to be able to answer that if you didn't even
>> start to describe what you actually did in gnuplot to get this
>> effect?
> 
> I am sorry that I didn't expand on details of the code. I was hoping
> that such an observation - meanwhile I'd just call it a bug[*] - is
> well known, so that there's already some standard hint to that. (Has
> that really never been observed before? Hard to believe, but anyway.)
> 
> What I did was defining a y-axis range with major tics=1 and minor
> tics=0.1 resolution, or, if you prefer actual code...
> 
>   set ytics 10
>   set mytics 2
>   set y2tics 1
>   set my2tics 10
> 
> The range of the y2 axis (where I observed the artifact) was defined
> as
> 
>   set y2r [0:6]

I am going to guess that you have misinterpreted what you are seeing in
the plot.   It is not an extra tic on any single axis.  Instead the
problem is that you are plotting two set of tics on each axis 
and since the end-points of the two axes do not match up,
neither do the tics.   

The crucial thing missing from the commands you show above is the "nomirror"
attribute.  Without it the y tics are drawn on both the right and left sides,
the y2 tics are also drawn on both the right and left sides, and
hilarity results when ymin != y2man  or ymax != y2max or both.

Note that unless you do somethine to tie them together, the y and y2
axes are scaled independently.

	Ethan






> 
> As said, I used a workaround to adjust the png size so that the
> rounding issues - as far as I suspect - eliminate each other. (Still
> can't believe, though, that this is how such elementary problems are
> to be countered with gnuplot.)
> 
> Thanks.
> 
> Janis
> 
> [*] I have a quite good idea how this type of bug is reflected in
> [gnuplot
> (or other application's) implementations.[**] (You can probably find
> it in "What Every Computer Scientist Should Know About Floating-Point
> Arithmetic".) What I'm wondering about, though, is that such an effect
> is observable in such a long time existing tool.
> 
> [**] Use the following code for various values (besides 0.1, e.g. 0.2,
> [0.25,
> 0.5, 0.05) and observe the final values
> 
>    i=0.0 ; while (i<1.0) i += 0.1 ; print i
> 
> many tools will not print 1.0 for an increment of 0.1, but, as
> expected, will print 1.0 for all the other values that I suggested
> above. There are of course various possibilities to avoid such FP
> problems if incrementing FP numbers in loops would not be done as
> primitive as depicted.

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Thread

Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-02 18:19 +0100
  Re: Major and minor ticks artifact Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2014-03-02 20:10 +0100
    Re: Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-14 23:54 +0100
      Re: Major and minor ticks artifact sfeam <sfeam@users.sourceforge.net> - 2014-03-14 22:17 -0700
        Re: Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-15 10:54 +0100
          Re: Major and minor ticks artifact Karl <mail.kfr@gmx.net> - 2014-03-18 18:38 +0100
            Re: Major and minor ticks artifact Hermann Peifer <peifer@gmx.eu> - 2014-03-20 07:10 +0100
      Re: Major and minor ticks artifact Hermann Peifer <peifer@gmx.eu> - 2014-03-15 13:27 +0100
        Re: Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-15 23:02 +0100
          Re: Major and minor ticks artifact Hermann Peifer <peifer@gmx.eu> - 2014-03-16 01:54 +0100
            Re: Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-21 05:52 +0100
          Re: Major and minor ticks artifact Dan Luecking <LookInSig@uark.edu> - 2014-03-20 12:24 -0500
            Re: Major and minor ticks artifact Janis Papanagnou <janis_papanagnou@hotmail.com> - 2014-03-21 05:54 +0100

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