How to make a line plot with a colorbar as the third variable?

Hello community,

Lets say I have three variables, being Y the variable one. X and Z are constant, of which Y depends on.

x= linspace(0,100,500);
z= [5, 15, 25, 35];

(I won't show the whole equations, so I'm just going to leave a made up function to demonstrate how all the variables influence each other)

for i = 1:length(z)
    K1 = konstant+ z(i);
    y(i,:) = (K1.*x)./((1 + (K1.*x)));
end

As an amateur in coding (general), I've seen similarish examples, but not one that could resemble to what I'm looking foward, which is shown below:

I know that is possible to apply the colormap function, but I'm having a bit of dificulties setting up the function, including the Ticks.

for i = 1:length(z)
    color = z(i,:);
    plot(x, y(i,:), 'color',color);
    h = colorbar('Ticks',0:0.25:1,'TickLabels',{'5','15','25','35'});

Something like this? All help is appeciated. Thank you.

Answer 1

[Ty Watkins]

You need to set the 'color' for each corresponding z value based on the colormap.

Given the equations you provided in your questions (though I added a value for konstant and changed the line for K1 so the lines would actually show up on the plot) here is a simple solution.

konstant = 0.01;

x= linspace(0,100,500);
z= [5, 15, 25, 35];

for i = 1:length(z)
    K1 = konstant * z(i);
    y(i,:) = K1.*x ./ (1 + K1.*x);
end

figure();
hold on;
grid on;
box on;

cmap = colormap('winter'); % take your pick (doc colormap)
zmap = linspace( min(z), max(z), length(cmap));

for i = 1:length(z)   
    color = interp1( zmap, cmap, z(i));
    plot(x, y(i,:), 'color',color);    
end

caxis([min(z), max(z)])
colorbar()

[Ty Watkins]

My solution seems to fit what you are trying to do, which is a single color for the entire line. Just separate colors for each line.

If, however, you are looking to color the line with a gradient based on a third array of values, you can use the suggestiongs provided @Bjorn Gustavsson.

I've also found a solution without extra functions from the exchange here. Though I had to add a 'drawnow' command before calling the colorbar for the lines to color correctly.

[André Silvestre]

This worked perfectly, thank you!

I also was plotting markers (specific Y values correspondent to experimental data), and it appears that those markers have different colors compared with the colors present in the colormap, shown below:

Each marker as a Y and Z associtated. Is there a way to color them to the correspondent Z color in the colorbar?

Thank you and Bjorn for the feedback, very appreciatted.

[Ty Watkins]

Yes, that can just as easily be done by getting the color code from the colorbar for the Z value of each data point.

mcolor = interp1( zmap, cmap, ZVALUE);

And then you can use this RGB triplet to set either the 'markerfacecolor' or the 'markeredgecolor' in the plot command.

plot(xdata, ydata), '+', 'markerfacecolor', mcolor, 'markeredgecolor', mcolor);  

If you have a set of ZVALUE's, the above code snippet will return the same size array of corresponding color values.

[André Silvestre]

Thank you!! Cannot express how much this helped me. Have a good day

Answer 2

[Bjorn Gustavsson]

When I want to plot colour-coded curves I use one of these functions from the file exchange:

cline, cline-m or plot-3d-color-line.

They should give you something to either use as is or take as a template for how to do it.

HTH

[Bjorn Gustavsson]

In addition to those tools I've also had good use of COLORMAP and COLORBAR utilities.

[André Silvestre]

Thank you!

Answer 3

[Image Analyst]

You need to have a colormap that is an N-by-3 array, not like your z which is a 1-by-4 array. Try this:

% Initialization Steps.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 18;
x = linspace(0,100,500);
z = [5, 15, 25, 35]/1000;
konstant = 0.00005;
% Create a colormap with as many colors as elements in z.
Lz = length(z);
cMap = jet(Lz);
% Create y matrix.
y = zeros(Lz, length(x));
for k = 1 : Lz
    K1 = konstant + z(k);
    y(k, :) = (K1.*x) ./ ((1 + (K1.*x)));
end
% Plot the different y curves.
for k = 1 : Lz
    thisColor = cMap(k,:);
    plot(x, y(k,:), 'color',thisColor, 'LineWidth', 4);
    hold on;
    tickLabels{k} = sprintf('%g', 1000 * z(k));
end
miny = min(y(:))
maxy = max(y(:))
caxis([miny, maxy])
grid on;
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
colormap(cMap);
h = colorbar('Ticks', linspace(miny, maxy, Lz), 'TickLabels', tickLabels);