Why axes handle deleted in Matlab loop? - matlab

Question

Code which tries to mimic the real dynamic condition
clear all; close all;
hFig2=figure('Units','inches', 'Name', 'Time');
hax2=axes(hFig2);
movegui(hFig2, 'southeast');
index=1;
while (index < 7);
hFig2=figure(hFig2);
u=0:0.01:1+index;
plot(hax2, u); % Give columns 1xXYZ to Matlab
hold on;
axis(hax2, 'xy');
axis(hax2, [0 (size(u,2)/1 - 0) min(u) max(u)]); % to maximise size
axis(hax2, 'off'); % no ticks
index=index+1;
pause(1);
hold off;
drawnow
end;
Logs 1 hax2 in more dynamic condition,
Logs 2 hax2 mostly in Code
%% Logs 1 in dynamic condition with failure output
% Failure in more dynamic conditions because axes get deleted for some reason
% hax2
%
% hax2 =
%
% handle to deleted Axes
%
%% Logs 2 mostly in Code condition and correct because
% hax2 =
%
% Axes with properties:
%
% XLim: [0 201]
% YLim: [0 2]
% XScale: 'linear'
% YScale: 'linear'
% GridLineStyle: '-'
% Position: [0.1300 0.1100 0.7750 0.8150]
% Units: 'normalized'
Error if failure in hax2 i.e. handle to deleted axes for some reason
%% Failure message
% Show all properties
%
% Warning: MATLAB has disabled some advanced graphics rendering features by switching to software OpenGL. For more information, click
% here.
% Error using plot
% Invalid handle.
%
% Error in test_invalid_handle (line 12)
% plot(hax2, u);
Some tentative proposals of solutions
Save the axes handle at the end of each loop; possible related thread Save axes handle when plotting In MATLAB
...
OS: Debian 8.5 64 bit
Matlab: 2016a
Hardware: Asus Zenbook UX303UA
Linux kernel: 4.6 of backports

Answer 1

When calling axes, the first input should be a parameter/value pair that specifies the parent. If you pass it a single handle graphics input it assumes that input is a handle to an axes
axes(hFig2)
% Error using axes
% Invalid axes handle
Or as you have it written
hax2 = axes(hFig2);
% Error using axes
% Too many output arguments.
Because you are passing an invalid axes handle to it, it doesn't properly assign the handle to a new axes to hax2. It is likely that your deleted hax2 that you're seeing is from a previous run of the script.
Instead, you'll want to use parameter/value pairs to specify the Parent property of the axes.
hax2 = axes('Parent', hFig2);
Also, I would remove the extraneous call to figure every time through the loop since you explicitly specify the parent object of each plot object