Problem with legend: colors don't match value of variable

hello, i have a problem with the legend in this script: i am doing subplots for the two parameters e and t, in every subplot e is fixed while t can vary between 5 different values. the problem is the legend doesn't match the colors. for instance, t= -50 should be red, -25 green, 0 blue, 25 light blue and t = 50 black, but the legend doesnt say this. Could anybody give me any suggestions on how to index the color and the value of the parameter so that they match? thank you

here is the code:

clear; clc; clf;

n = 1001;

x = linspace(-100, 100, n);

y = linspace(-100, 100, n);

[X, Y] = meshgrid(x, y);

clr = ['r','g','b','c','k'];

a = 4;

e = [-50 -10 0 50];

t = linspace(-50, 50, 5);

LegendsStrings = cell(length(t),1);

for q = 1:a

for r = 1:5

Z = fn(X, Y, e(q), t(r), n);

subplot(2, 2, q)

xline(0, 'Color', 'k', 'LineWidth', 0.5);

yline(0, 'Color', 'k', 'LineWidth', 0.5);

hold on

v = [0, 0];

contour(X, Y, Z, v, 'LineWidth', 1.5, 'LineColor', clr(r))

xlabel('x')

ylabel('y')

title("e = " + e(q))

grid on

axis equal

hold off

LegendsStrings{r} = ['t = ', num2str(t(r))];

end

legend(LegendsStrings, 'Interpreter', 'none')

end

function Z = fn(X,Y,e,t,n)

Z = zeros(n, n);

B = X + Y + e + t;

D = X.*Y - e.*t;

for i= 1:n

for j= 1:n

if B(i,j) >= 0

Z(i,j) = D(i,j);

else

Z(i,j) = -1;

end

end

end

end

[LUCA D'AMBROSIO]

update: i tried the following, now the colors match but the legend adds some unused lines

n = 101;

x = linspace(-100, 100, n);

y = linspace(-100, 100, n);

[X, Y] = meshgrid(x, y);

clr = ['r','g','b','c','k'];

a = 4;

e = [-50 -10 0 50];

t = linspace(-50, 50, 5);

LegendsStrings = cell(numel(t),1);

for q = 1:a

for r = 1:5

Z = fn(X, Y, e(q), t(r), n);

subplot(2, 2, q)

xline(0, 'Color', 'k', 'LineWidth', 0.5);

yline(0, 'Color', 'k', 'LineWidth', 0.5);

hold on

LegendsStrings{r} = ['t = ', num2str(t(r))];

v = [0, 0];

contour(X, Y, Z, v, 'LineWidth', 1.5, 'LineColor', clr(r), 'DisplayName', LegendsStrings{r})

xlabel('x')

ylabel('y')

title("e = " + e(q))

grid on

axis equal

hold off

% xp = [-95, -80];

% yp = (-30-12*r)*ones(1, 2);

% plot(xp, yp, ['-', clr(r)])

% text(xp(2)+5, yp(2),['t = ', num2str(t(r))],'FontSize',8)

end

legend()

end

Answer 1

[Star Strider]

I can’t run this since ‘fn’ is missing.

n = 101;
x = linspace(-100, 100, n);
y = linspace(-100, 100, n);
[X, Y] = meshgrid(x, y);
clr = ['r','g','b','c','k'];
a = 4;
e = [-50 -10 0 50];
t = linspace(-50, 50, 5);
LegendsStrings = cell(numel(t),1);
for q = 1:a
    for r = 1:5
        Z = fn(X, Y, e(q), t(r), n);
        subplot(2, 2, q)
        xline(0, 'Color', 'k', 'LineWidth', 0.5);
        yline(0, 'Color', 'k', 'LineWidth', 0.5);
        hold on
        LegendsStrings{r} = ['t = ', num2str(t(r))];
        v = [0, 0];
        hc(r) = contour(X, Y, Z, v, 'LineWidth', 1.5, 'LineColor', clr(r), 'DisplayName', LegendsStrings{r});
        xlabel('x')
        ylabel('y')
        title("e = " + e(q))
        grid on
        axis equal
        hold off
        
        % xp = [-95, -80]; 
        % yp = (-30-12*r)*ones(1, 2);
        % plot(xp, yp, ['-', clr(r)])
        % text(xp(2)+5, yp(2),['t = ', num2str(t(r))],'FontSize',8)    
    end
    legend(hc, 'Location','best')
     
end

Unrecognized function or variable 'fn'.

That aside, I propose a solution, that being to create a handle to the contours you want, and then pass them to your legend call. (I will test this when ‘fn’ appears. In the interim, I leave that to you)

.

[LUCA D'AMBROSIO]

i posted the function fn above.

i don't know if probably isnt visualized correctly, here i attach it again:

function Z = fn(X,Y,e,t,n)

Z = zeros(n, n);

B = X + Y + e + t;

D = X.*Y - e.*t;

for i= 1:n

for j= 1:n

if B(i,j) >= 0

Z(i,j) = D(i,j);

else

Z(i,j) = -1;

end

end

end

end

[Star Strider]

I just looked at the code in your Comment.

n = 101;
x = linspace(-100, 100, n);
y = linspace(-100, 100, n);
[X, Y] = meshgrid(x, y);
clr = ['r','g','b','c','k'];
a = 4;
e = [-50 -10 0 50];
t = linspace(-50, 50, 5);
LegendsStrings = cell(numel(t),1);
for q = 1:a
    for r = 1:5
        Z = fn(X, Y, e(q), t(r), n);
        subplot(2, 2, q)
        xline(0, 'Color', 'k', 'LineWidth', 0.5);
        yline(0, 'Color', 'k', 'LineWidth', 0.5);
        hold on
        LegendsStrings{r} = ['t = ', num2str(t(r))];
        v = [0, 0];
        [~,hc{r}] = contour(X, Y, Z, v, 'LineWidth', 1.5, 'LineColor', clr(r), 'DisplayName', LegendsStrings{r});
        % hc{r}
        xlabel('x')
        ylabel('y')
        title("e = " + e(q))
        grid on
        axis equal
        hold off
        % xp = [-95, -80]; 
        % yp = (-30-12*r)*ones(1, 2);
        % plot(xp, yp, ['-', clr(r)])
        % text(xp(2)+5, yp(2),['t = ', num2str(t(r))],'FontSize',8)    
    end
    % legend([hc{:}], 'Location','best')
    if q == a
        hl = legend([hc{:}]);
    end
end

sppos = [subplot(2,2,2).Position; subplot(2,2,4).Position];
lpos = hl.Position;
hl.Position = [sppos(1,1)+sppos(1,3) mean(sppos(:,2))+sppos(1,4)*0.25 lpos(3)*0.85 lpos(4)];

function Z = fn(X,Y,e,t,n)
    Z = zeros(n, n);
    B = X + Y + e + t;
    D = X.*Y - e.*t;
    
    for i= 1:n
        for j= 1:n
            if B(i,j) >= 0
                Z(i,j) = D(i,j);
            else 
                Z(i,j) = -1;
            end
        end
    end
end

This appears to elilminate the extraneous llines. I did my best to get the legend to be narrower so that it fits, however the third position argument to it (‘width’) does not appear to be working correctly here. (It may work correctly in your code.)

.

[LUCA D'AMBROSIO]

thank you very much, it works very well. thank you

[Star Strider]

As always, my pleasure!