help debugging 3-D plot code

Question

Brendan Clark 2021-4-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/804406-help-debugging-3-d-plot-code

评论： Bjorn Gustavsson 2021-4-18

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

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Brendan Clark 2021-4-16

ope, good catch

its supposed to be

x=a*cos(φ)sin(θ);

y=b*cos(φ)sin(θ);

z=b*sin(φ);

when i corrected the cos to sin that was incorrect I ended up with a 2d graph on the 3d plan, what were the corrections that you made?

Clayton Gotberg 2021-4-17

Check your new equations again! Now, x and y are defined the same.

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Answer 1

Bjorn Gustavsson 2021-4-17

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/804406-help-debugging-3-d-plot-code#answer_677791

在 MATLAB Online 中打开

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

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Brendan Clark 2021-4-18

Thank you. This would be the third typo I've found in my homework assignment for this week. What I posted for the equations with x and y being the same was copy and pasted from my hw. The right equation did the trick.

Bjorn Gustavsson 2021-4-18

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.

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