How to draw this 3D plot (PSD cone)

Hi all:

I have vectors: x,y,z with the same dimension.

I use plot(x,y,z,',') to plot it. The following is the code:

clear all;                   
close all;
clc
num = 0;
%%loop
for x = 0 : .02 : 1
  for y = -1 : .02 : 1
      for z = 0 : .02 : 1
          num = num + 1;
          A = [x y;y z];
          a = eig(A);
          if (a(1) >= 0) && (a(2) >= 0)
              vecx(num) = x;
              vecy(num) = y;
              vecz(num) = z;
          else
              vecx(num) = NaN;
              vecy(num) = NaN;
              vecz(num) = NaN;
          end
      end
  end
end
%%picture
figure(1)
plot3(vecx,vecy,vecz,'.')
axis([0 1 -1 1 0 1])

The answer should look like:

However, my answer is:

The similar shape, but different result. How to fix it?

How to draw the lines on the surface?

Thanks,

Answer 1

[Stefan Reich]

Dear Dian-Jing, Usually I would suggest using

meshgrid()
surf()

In your case, downloading and installing this file might just be easier! https://www.mathworks.com/matlabcentral/fileexchange/5105-making-surface-plots-from-scatter-data Best, S