# help debugging 3-D plot code

1 view (last 30 days)
Brendan Clark on 16 Apr 2021
Commented: Bjorn Gustavsson on 18 Apr 2021
I'm trying to figure out why this ellipsoid plot isn't working the way it's supposed to.
It seems that the grid direction may be wrong, but every way that I've tried to change it changes the plot in other undesirable ways as well.
I'm not allowed to use the ellipsoid function, I have to use meshgrid, its very close to correct, but isn't.
The code thus far is.
clear variables
clc
[phi,theta] = meshgrid(linspace(0,2*pi,20),(linspace(0,pi,20)));
figure(1)
a=1;
b=.5;
x=a*cos(phi).*cos(theta);
y=b*cos(phi).*sin(theta);
z=b*sin(phi);
surf(x,y,z);
hold on
AZ=-13;
EL=28;
view(AZ,EL)
xlabel('x')
ylabel('y')
zlabel('z')
title('Ellipsoid')
set(gca, 'XTick',[-0.8,-0.6,-0.4,-0.2,0,0.2,0.4,0.6,0.8])
set(gca, 'YTick',[-0.4,-0.2,0,0.2,0.4])
when run the code produces
what I need is
Clayton Gotberg on 17 Apr 2021
Check your new equations again! Now, x and y are defined the same.

Bjorn Gustavsson on 17 Apr 2021
You have to get your equations for x, y and z right:
x = a*cos(phi).*sin(theta);
y = b*sin(phi).*sin(theta);
z = b*cos(theta);
surf(x,y,z);
HTH
##### 2 CommentsShowHide 1 older comment
Bjorn Gustavsson on 18 Apr 2021
When I have these sorts of typo-problems I find that printing the code out on paper and annotate it by hand with circling in, crossing over and connecting variables and statements to be helpful. If you see what you think that you've written and not what you've actually written then that helps - sometimes.