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Groups > comp.graphics.apps.gnuplot > #2345

Re: Major and minor ticks artifact

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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]

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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