Matlab: Plot3 not showing the 3rd axis

Question

All the three variables I am using to plot are matrix of size 1x1x100. I am using this code line to plot:

hold on; 
for i=1:100
    plot3(R_L(:,:,i),N_Pc(:,:,i),CO2_molefraction_top_of_window(:,:,i),'o');
    xlabel('R_L');
    ylabel('N_P_c');
    zlabel('CO_2')
end

However, I am not getting the third axis, and hence the third variable CO2_molefraction_top_of_window on the plot. May I know where am I wrong?

Besides the above question, but on the same subject, I want to know if there is any option where I can plot 4 dimensional plot just like the 3 dimensional plot which can be drawn using plot3?

Answer 1

So I had the same problem when using plot3. For some reason, using the hold on command "flattens" the plot. I'm not sure why, but I suspect it has something to do with the operation hold on performs on the plot. Edit: To clarify, the 3d plot is still there, but the perspective has been forced to change. If you use the "rotate 3D" tool (the one with an arrow around a cube), you can see the graph is 3d, the default perspective is just straight on so only two axes are visible and it appears flat.

Answer 2

I came across a similar problem and as @Drofdarb's the hold on seems to flatten out one axis. Here is a snippet of my code, hope this helps.

for iter = 1:num_iters:
    % hold on;
    grid on;
    plot3(tita0,tita1, num_iters,'o')
    title('Tita0, Tita1')
    xlabel('Tita0')
    ylabel('Tita1')
    zlabel('Iterations')
    hold on;            % <---- Place here
    drawnow   
end

---

As opposed to:

for iter = 1:num_iters:
    grid on;
    hold on;          % <---- Not here
    plot3(tita0,tita1, num_iters,'o')
    title('Tita0, Tita1')
    xlabel('Tita0')
    ylabel('Tita1')
    zlabel('Iterations')
    % hold on;
    drawnow   
end

Answer 3

Just a note --- you only need to do the xlabel ylabel zlabel commands once (outside the loop).

Also:

• is there any reason your matrices are 1x1x100 instead of just 100x1 or 1x100? Because if you reshape them to 2D you can just do the plotting in one hit.
• What do you mean by "missing third axis"? When I run your code (or as close as I can get, since you didn't provide a reproducible example), I do get a 3rd axis:

.

X = rand(1,1,100); % 1x1x100 X matrix
Y = rand(1,1,100); % 1x1x100 Y matrix
Z = rand(1,1,100); % 1x1x100 Z matrix
% Now, we could do a for loop and plot X(:,:,i), Y(:,:,i), Z(:,:,i),
% OR we can just convert the matrix to a vector (since it's 1x1x100 anyway)
%    and do the plotting in one go using 'squeeze' (see 'help squeeze').
%    squeeze(X) converts it from 1x1x100 (3D matrix) to 100x1 (vector):
plot3(squeeze(X),squeeze(Y),squeeze(Z),'o')
xlabel('x')
ylabel('y')
zlabel('z')

This gives the following, in which you can clearly see three axes:

If it's the gridlines that you want to make the graph look "more 3D", then try grid on (which is in the examples in the Matlab help file for plot3, try help plot3 from the Matlab prompt):

grid on

You will have to clarify "missing third axis" a bit more.