[Octave-bug-tracker] [bug #52206] semilogy speed

[Petr Mikulik]

URL:
  <http://savannah.gnu.org/bugs/?52206>

                 Summary: semilogy speed
                 Project: GNU Octave
            Submitted by: mikulik
            Submitted on: Wed 11 Oct 2017 08:50:51 AM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.1
        Operating System: GNU/Linux

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Details:

Hello,

well, this is either a performance regression or a bug.

Using a graphical update during a simulation, I have found a major slow-down
of the "semilogy" plot in Octave 4.2.1 compared to other Octave versions (40
times compared to 4.0.3).

For this test code:


n=100;
x=(1:n)';
y=1+10*rand(n,4);
tic
for k=1:10
    semilogy(x,y)
end
toc


the execution times are:


Octave 2.1.73   0.014 sec
Octave 3.6.4    0.68  sec
Octave 4.0.3    0.15  sec
Octave 4.2.1    6     sec
Octave 4.3.0+   0.84  sec


Using  plot(x,log10(y))  instead of semilogy() gives


Octave 2.1.73   0.014 sec
Octave 3.6.4    0.68  sec
Octave 4.0.3    0.15  sec
Octave 4.2.1    0.26  sec
Octave 4.3.0+   0.65  sec


Execution times are similar for all 3 backends.
Gnuplot itself does a similar plot in 0.01 sec.


Can you please fix it for Octave 4.2.2?

Why the performance dropped so much from 4.0.3 (4x for plot, 6x for
semilogy)?

The above test further shows slow down of plot() in Octave 4.3.0+ .

Can the the plotting be improved?

Thanks.





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