[Octave-bug-tracker] [bug #56983] Plotting constant values with small noise gives erratic results

[Roland Baudin]

URL:
  <https://savannah.gnu.org/bugs/?56983>

                 Summary: Plotting constant values with small noise gives
erratic results
                 Project: GNU Octave
            Submitted by: roland65
            Submitted on: mer. 02 oct. 2019 14:15:15 UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.1
        Operating System: Any

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Details:

Here is the problematic code:

close all;
clear all;
s = 1e-3;
x = 100 * ones(1, 1000) + s * randn(1, 1000);
plot(x);

When s is higher than 1e-6, this plots (as expected) a noise around the mean
value 100.

When s = 1e-6, this plots a line that is sometimes at the top of the figure,
or at the bottom, or there is no line at all. The figure frame is corrupted,
etc. (see screenshot1).

When s = 1e-8, there is sometimes no frame in the figure. The line is often
not displayed (see screenshot2).

When s <= 1e-10, the plot correctly displays a line in the middle of the
figure and the frame is also displayed, as expected.

I was able to reproduce this issue in Octave 4.2.1 (windows), 4.4.1 (windows),
5.1.0 (windows), 5.1.0 (Ubuntu Linux 18.04).

The problem is the same with qt or fltk toolkit. I didn't test with Gnuplot.





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