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is it a bug?

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G A
G A on 11 Sep 2019
Commented: G A on 11 Sep 2019
The code below
(i) does not produce an error message about not matching x and y; it can be explained by implicit expansion in plot();
(ii) produces 100 legends; this I cannot explain.
x=1:100;
y=1;
plot(x,y,'DisplayName','a bug'),
legend('-DynamicLegend'),

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Accepted Answer

Steven Lord
Steven Lord on 11 Sep 2019
If you call plot with an output argument to return handles to any lines that are created, you'll see that 100 individual lines get created, one per point.
x=1:100;
y=1;
h = plot(x,y,'DisplayName','a bug');
size(h)
That's also why your legend has 100 entries, one per line that plot created.
If you're using release R2018b or later and you want to display a horizontal line stretching the whole width of the axes, use yline.

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G A
G A on 11 Sep 2019
You can use yline within the existing axes, which are defined automatically in my case by plot(x,y). How would you use yline instead the following?
plot(x,y*ones(size(x)),'DisplayName','leg')
Steven Lord
Steven Lord on 11 Sep 2019
I'm not completely sure I understand what you're asking in your first sentence. If you want to know how to use yline with the DisplayName property, that's easy.
axis([1 10 1 10]);
xline(7, 'DisplayName', 'x = 7', 'Color', 'r');
yline(pi, 'DisplayName', 'y = pi', 'Color', 'k');
legend show
Or do you want a line with markers at certain x values and/or only spanning part of the axes? If so yline isn't the right tool for that job. For that you would do what you described:
x = 1:10;
y = ones(size(x));
h = plot(x, y, ':d', 'DisplayName', 'Dotted line with diamonds');
legend show
G A
G A on 11 Sep 2019
Sorry for my English. In the first sentence I was asking the following:
xlim([x(1) x(end)]);
yline(pi, 'DisplayName', 'y = pi', 'Color', 'k');
legend show
y-axis is defined automatically.

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More Answers (1)

Bruno Luong
Bruno Luong on 11 Sep 2019
Edited: Bruno Luong on 11 Sep 2019
No it's not a bug: from PLOT doc
  • If one of X or Y is a scalar and the other is either a scalar or a vector, then the plot function plots discrete points. However, to see the points you must specify a marker symbol, for example, plot(X,Y,'o').
You get really 100 points plotted.

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