Legend not showing in MATLAB 2020b but works in 2023b

The following MATLAB script plots multiple scatter points and a filled polygon, adding them dynamically in a loop. I use the DisplayName property for legend entries and then create a legend using an array of handles.

The legend displays correctly in MATLAB 2023b, but in MATLAB 2020b, the legend does not appear.

% Test data
x=rand(1,10);
y=rand(1,10);

iterationNumber = 2;
A=rand(iterationNumber,10);
B=rand(iterationNumber,10);
C=rand(iterationNumber,10);
D=rand(iterationNumber,10);

% Proper polygon for fill
z = [0 4 5 2 1];
w = [0 0 2 4 3];

fig = figure;
hold on;
grid on;

h1 = scatter(x, y, 'DisplayName', 'XY Points');
h2 = fill(z, w, 'r', 'DisplayName', 'Polygon');

handles = [h1 h2];
for idx = 1:iterationNumber
    h3 = scatter(A(idx,:), B(idx,:), 'DisplayName', sprintf('Mode %d', idx));
    h4 = scatter(C(idx,:), D(idx,:), 'DisplayName', 'Potential');
    handles = [handles h3 h4];
end

xlabel('xLabel');
ylabel('yLabel');

legend(handles);

hold off;

Is there a difference in how DisplayName and legend(handles) are handled between MATLAB 2020b and newer versions? What is the recommended way to ensure that legends show correctly in older versions?

[Torsten]

Look at the version history of the legend command at the bottom of this page:

https://uk.mathworks.com/help/matlab/ref/legend.html

Although I cannot directly see what causes the legend command fail in R2020b in your case, it shows that there were several changes between 2020 and 2023.

[dpb]

I don't see anything fatal, either.

FYI the legend shows for both R2019b and R2021b; but I don't have R2020b installed.

Have you installed the latest patches on your installation?

What if you set breakpoint and then interactively work with legend() to put on individually; maybe a symptom will show up to explain the problem.

ADDENDUM

Since all handles are being included, don't need the handles array; have you tried simply

legend

w/o any argument?

[dpb]

Just one refinement to preallocate the handles array although with only a small number as here the dynamic reallocation won't be a noticeable overhead...

...
iterationNumber = 2;
...
h=gobjects(2+2*iterationNumber,1);      % preallocate for graphics object handles
h(1) = scatter(x, y, 'DisplayName', 'XY Points');
h(2) = fill(z, w, 'r', 'DisplayName', 'Polygon');
j=2;                                    % counter for handles
for idx = 1:iterationNumber
  j=j+1;
  h(j) = scatter(A(idx,:), B(idx,:), 'DisplayName', sprintf('Mode %d', idx));
  j=j+1;
  h(j) = scatter(C(idx,:), D(idx,:), 'DisplayName', 'Potential');
end
legend(h);
...

[Walter Roberson]

Datapoint:

The code shows the legend for me on MacOS 15.6.1 for Intel

[Cris LaPierre]

As an addtiional datapoint, when I run the code in R2020b, the legend appears. I am using Windows 11.

[dpb]

@Florian - just out of curiosity, what does

hLg=findobj(gcf,'type','legend');
hLg.Interpreter

return

[Florian]

Indeed, when I run it now in R2020b, the legend appears. The issue was solved when I ran clear, clc. I though that handles would be freshly initialized when running the script, but apparently some old version of handles was still in memory yesterday.