Labelling Curves on a Graph, This code worked a decade ago, but will not work in 2023a

This code worked fine a decade ago, but will not work in 2023a

X = [0	1100	1600	2400	2400	2800	3400	3800];
Y = fliplr(X);
figure
    hold on
    C(1, 1) = 100; % data value to plot on the line
    C(2, 1) = length(X); % number of data points
    C(1, 2 : length(X)+1) = X; % x data points for the line
    C(2, 2 : length(X)+1) = Y; % y data points for the line
    h_b = plot(X, Y, '-b', 'LineWidth', 2);
    clabel(C, h_b, 'LabelSpacing', 1000)

It now results in

"Error using clabel

Not enough contour handles."

A decade ago I got the original idea from: https://stackoverflow.com/questions/19319455/matlab-graph-plotting-legend-and-curves-with-labels

and it worked fine. It made a graph similar to:

Now the clabel command errors and I can't figure out how to fix it. Any help would be appreciated.

Answer 1

[Star Strider]

Looking at the current clabel documentation, the second argument to it has to be the second output of the contour call. It is likely looking for information in ‘h_b’ that does not exist because it is a plot handle and not a contour handle. (MATLAB has changed significantly in the past decade.)

.

[Craig]

Hi Star Strider, Thanks for the reply! Any ideas on how to work around this, or to accomplish the same thing (putting in-line labels on line plots automatically without having to calculate the text coordinates)?

[Star Strider]

My pleasure!

The only aproach I can think of is to recalculate the contours using contour and then use its outputs. (It would probably also be necessary to significantly update the rest of the code.) The current online documentation only goes back to R2018b, and that is likely newer than the decade-old version you are using.

Aside from that, you could probably use the text function, however it would be necessary to write your own supporting code (calculating the rotation angles and such), as well as code to determine the positions of the text objects. (I chose the second and second-to-last coordinate positions here.)

Example —

X = [0	1100	1600	2400	2400	2800	3400	3800];
Y = fliplr(X);
figure
    hold on
    C(1, 1) = 100; % data value to plot on the line
    C(2, 1) = length(X); % number of data points
    C(1, 2 : length(X)+1) = X; % x data points for the line
    C(2, 2 : length(X)+1) = Y; % y data points for the line
    h_b = plot(X, Y, '-b', 'LineWidth', 2);
    % clabel(C, h_b, 'LabelSpacing', 1000)
    % a = atan2d(diff(Y), diff(X));                               % Rotation Angles
    a = atan2d(gradient(Y), gradient(X));                       % Rotation Angles
    kv = [2 7];
    for k = 1:numel(kv)
        text(X(kv(k)), Y(kv(k)), "100", 'Rotation',a(kv(k)), 'BackgroundColor','w', 'FontSize',14)
    end

EDIT — (7 Jan 2024 at 15:45)

Substituted gradient for diff in the ‘a’ calculations. It gives a better result, and the output is the same size as the input, so the indices now match. (My apologies for not using it originally.)

.

[Craig]

That looks like it will work, Thanks for your help!

[Star Strider]

As always, my pleasure!