Custom contour level labeling not working

I am trying to match my papers resutls with another and the way they label their contours is with a bit of an offset (screenshot of table). I m trying to find a way to be able to sort of overide the clabel so for a value of 0.5 for example it displays 1 as per the table in the paper. levels1 are my plotting lines and levels2 is what i want to use for labeling the lines. Doing it this way it just puts the labels at the "correct value levels"

levels1 = [-3  -2  -1  -0.5   0   0.5   1   2   3   4   5];
levels2 = [-4  -3  -2   -1    0    1    2   3   4   5   6];

% 1) Plot background (if you have one)
if Re == 400
    bg = imread('comp.png');
else
    bg = imread('Re_1000wcont.png');
end
bg = flipud(bg);
figure
imagesc([0 1],[0 1], bg);
set(gca,'YDir','normal');
hold on;


[C, hLine] = contour( ...
    X, Y, -flipud(omega), ...
    levels1, ...
    'LineColor','b', 'LineStyle','--', 'LineWidth',1 );
axis equal;  box on;  xlim([0 1]);  ylim([0 1]);
hold on;


clabel(C, hLine, levels2, ...
       'FontSize',    13, ...
       'LabelSpacing',300, ...
       'Color',       'r');


xlabel('$x$', 'Interpreter','latex');
ylabel('$y$', 'Interpreter','latex');
ax = gca;
ax.TickLabelInterpreter = 'latex';

Answer 1

[Benjamin Kraus]

Assuming you are using MATLAB R2022b or newer, I would recommend leveraging the LabelFormat property, which lets you specify a custom function for generating your labels.

If you set the value of LabelFormat to a function handle, then the function is called with a vector containing all the levels. You can control the output, which should be a string vector of the same size. Whatever strings are returned are used as the labels on the lines.

I don't have your raw data, so I'll give an example with made-up data.

function labels = adjustValues(vals)
% Start by assuming each label will reflect the actual value.
labels = string(vals);

% Replace -0.5 and 0.5 with -1 and 1:
labels(vals == 0.5) = "1";
labels(vals == -0.5) = "-1";

% Replace -1 to -3 with -2 to -4.
labels(vals <= -1) = string(vals(vals <= -1)-1);

% Replace 1 to 5 with 2 to 6.
labels(vals >= 1) = string(vals(vals >= 1)+1);
end

[X,Y] = meshgrid(linspace(0,pi,50));
Z = (cos(X).*sin(Y))*6;
contour(Z, [-3:-1 -0.5 0 0.5 1:5], ShowText=true, LabelFormat=@adjustValues)

●

[Les Beckham]

Maybe I'm missing something, but this part of your code doesn't seem to be working (there is no contour labeled 1 or -1):

% Replace -0.5 and 0.5 with -1 and 1:
labels(vals == 0.5) = "0.5";
labels(vals == -0.5) = "-0.5";

Perhaps due to violating the rule to never compare floats for equality?

[Benjamin Kraus]

@Les Beckham: Good catch. That was just a mistake in my code. I've fixed it now.

[Derik]

Thank you so much this worked great!