[Octave-bug-tracker] [bug #58566] plotyy() and subplot() generate errors

[Neil Konzen]

URL:
  <https://savannah.gnu.org/bugs/?58566>

                 Summary: plotyy() and subplot() generate errors
                 Project: GNU Octave
            Submitted by: waterdog1
            Submitted on: Sun 14 Jun 2020 12:15:03 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error
                  Status: None
             Assigned to: None
         Originator Name: waterdog1
        Originator Email: 
             Open/Closed: Open
                 Release: 5.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows

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Details:

The following code shows two problems.  plotyy() generates a ton of 'error:
get: invalid handle (= -1850.04)' warnings, and the first of four plot traces
in each subplot aren't shown.  If the 'hold on' is commented out, then the
subplot() window partitioning is ignored and only single chart is drawn.

The problem seems related to using subplot() to re-select a subplot that has
already been plotted into; i.e. the second pass through the ia loop below.

Neither problem occurs if plot() is used instead of plotyy().


function chart_prob
  close all; figure;
  x = linspace(0,10,10);
  y = rand(4*4,10);
  for ia=1:2
    for ip=1:4
      subplot(2,2,ip);
      % hold on is commented, only 1 window-sized chart
      % is drawn: subplot above is ignored().
      hold on;
      grid on;
      iy = (ia-1)*4 + ip;
      % plot(x,y(iy,:)); does the right thing
      plotyy(x,y(iy,:), x,y(iy+1,:));
    end
  end
end


The only workaround I could find was to swap the for-ia and for-ip/subplot
lines, so that subplot() is only called once per chart area.  Alas this is
extremely difficult to do in my particular application: any other workaround
ideas would be appreciated.





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