hey guys im trying to plot this in 3D but i keep getting an error, "Data cannot have more than 2 dimensions."

here is my code;

% 1) Compute the volume of a cylindrical shell with an inner radius
% r1=5,
% an outer radius
% r2=6, and length=10.

r1 = 5;     %inner radius 
r2 = 6;     %outer radius
h  = 10;    %height 

dr   = 0.01; 
dz   = 0.1; 
dphi = 0.01; 

% set vector of iteration
r   = [r1:dr:r2];
z   = [0:dz:h];
phi = [0:dphi:2*pi];

noi_r   = length(r); 
noi_phi = length(phi); 
noi_z   = length(z);

x = zeros(noi_r,noi_phi,noi_z);
y = zeros(noi_r,noi_phi,noi_z);
z = zeros(noi_r,noi_phi,noi_z);
plot3(NaN,NaN,NaN,'.')
hold on

%initial volume 
Volume =0; 
for ir = 1:noi_r
    for iphi = 1:noi_phi
        for iz = 1:noi_z
            dv = r(ir)*dphi*dz*dr;
            Volume = Volume +dv;
            x(ir,iphi,iz) = r(ir)*cos(phi(iphi));
            y(ir,iphi,iz) = r(ir)*sin(phi(iphi)); 
            z(ir,iphi,iz) = z(iz); 
            plot3(x,y,z,'.')
          
        end
       
    end
     
end
hold off

disp('volume is = ')
disp(Volume)

[Image Analyst]

What is your intent with this?

plot3(NaN,NaN,NaN,'.')

[boutros baqain]

Is to create a 3D plot :). But it won’t work. I can’t plot the XYZ

Answer 1

[David K.]

So the issue is that plot3 takes either a vector or a 2d matrix. Since you are plotting it as points you do not actually need to make your x,y, and z 3 dimensional. If you wanted you could have them as one long vector. So, to fix your issue you can do a few things. First, change your plot3 to

plot3(x(ir,iphi,iz),y(ir,iphi,iz),z(ir,iphi,iz),'.')

However, plotting this many times in a loop is extremely slow. Instead, after the loop you can do this

plot3(x(:),y(:),z(:),'.')

However, right now, your code will create a cylindrical shell at z = 0 and not have any height to it. This is because you are overwriting your z vector with zeros. I would suggest changing those names so you can have it be the proper height.

[boutros baqain]

Hi David, what do u suggest changing the names of the z vector to? I’ve tried few things but don’t get a full shell. Thank you!

[David K.]

When I was testing before I just did z1. In the code I put the comments to point out what z affects. Since (5) had z(iz), it was expecting the z to still be assigned to (1). So to avoid overwriting it in (3) you have to change the previous z names to z1. Then, since you still want z1 in (5) you change that.

z1   = [0:dz:h];%%%%%%  (1)
phi = [0:dphi:2*pi];
noi_r   = length(r); 
noi_phi = length(phi); 
noi_z   = length(z1);%%%%%   (2)
x = zeros(noi_r,noi_phi,noi_z);
y = zeros(noi_r,noi_phi,noi_z);
z = zeros(noi_r,noi_phi,noi_z);%%%%%%%   (3)
plot3(NaN,NaN,NaN,'.')
hold on
%initial volume 
Volume =0; 
for ir = 1:noi_r
    for iphi = 1:noi_phi
        for iz = 1:noi_z%%%%%   (4)
            dv = r(ir)*dphi*dz*dr;
            Volume = Volume +dv;
            x(ir,iphi,iz) = r(ir)*cos(phi(iphi));
            y(ir,iphi,iz) = r(ir)*sin(phi(iphi)); 
            z(ir,iphi,iz) = z1(iz);%%%%%%%   (5)         
        end
    end
end
plot3(x(:),y(:),z(:),'.')

[boutros baqain]

Thank you very much

Answer 2

[boutros baqain]

Thank you so much David k. I will try what you’ve suggested. Thank you!