Plotting 4D matrix in 2D space

Hi,

I would like to plot a scatter plot of 4D points in a 2D plane.

This is the line out of my code that I am using:

plot(data(:,1),data(:,2), data(:,3), data(:,4), 'k.');

Whenever I plot the data, some of it plots and some of it ends up with random lines of garabage.

Attached is a screenshot of the results that I am getting by using the above line of code.

How can I get this to be plotted in 2D?

Thanks!

Answer 1

[the cyclist]

You are using the plot command in a way that you wish it worked, without carefully understanding how the syntax actually works. You cannot just put in four columns of data into a command, and hope it does what you want.

Here is some simplified data, and your plotting code:

data = [1 1 4 4;
        2 3 5 6;
        3 2 6 5];
figure
h = plot(data(:,1),data(:,2), data(:,3), data(:,4),'k.');
set(h,'MarkerSize',16) % Adding this to make the dots more visible

If you carefully read the documentation you will see that your code is plotting two pairs of data against each other: data(:,1) vs. data(:,2), and data(:,3) vs. data(:4). Then you add a 'LineSpec' (black dots) to the second pair of plots, while the first set uses the default, which is a blue line.

This code is functionally equivalent to

data = [1 1 4 4;
        2 3 5 6;
        3 2 6 5];
figure
hold on
plot(data(:,1),data(:,2)); % First plot, default to blue line connecting points
h = plot(data(:,3), data(:,4),'k.'); % Second plot, using black dots
set(h,'MarkerSize',16)

It's not clear to me what you actually want the plot to be. If you want the projection of the the 4-dimensional data onto 2 dimensions, then I believe you simply ignore the 3rd and 4th dimension, and plot

figure
h = plot(data(:,1),data(:,2),'k.');
set(h,'MarkerSize',16)