How to plot sphere in sphere coordinates?

I'm just trying to plot known sphere coordinates:

function sphere(r)
phi = linspace(0,2*pi);
theta = linspace(0,pi);
x = r*cos(phi).*sin(theta);
y = r*sin(phi).*sin(theta);
z = r*cos(theta);
plot3(x,y,z)
end

However this isn't doing the trick. What have I mathematically confounded?

Answer 1

[J. Alex Lee]

Your problem is not with conversion or plotting, but defining the coordinates that you want...

[phi,theta] = meshgrid(linspace(0,2*pi),linspace(0,pi));

Also if you didn't know:

https://www.mathworks.com/help/matlab/ref/sph2cart.html

[Niklas Kurz]

yea, but I wanted to go through the rough way ;)

You could have said additionally that I need to swap plot3(x,y,z) with mesh(x,y,z), but all in all you've been nudging me in the right direction. Thx

[J. Alex Lee]

sure thing. if you decide you don't want the rough way and you haven't seen it, check

https://www.mathworks.com/help/matlab/ref/sphere.html

[X,Y,Z] = r*sphere(n)
mesh(X,Y,Z)
% surf(X,Y,Z) % filled in faces

Also check out

https://www.mathworks.com/matlabcentral/fileexchange/50105-icosphere

Answer 2

[Bruno Luong]

function sphere(r)
phi = linspace(0,2*pi);
theta = linspace(0,pi).'; % first change
x = r*cos(phi).*sin(theta);
y = r*sin(phi).*sin(theta);
z = r*cos(theta)+0*phi; % second change, make z same-size 2d array as x and y
plot3(x,y,z);
end

[J. Alex Lee]

nice. might be confusing depending on the audience though :)

As a side note, I wish plot also supported "implicit expansion" so you don't have to make the second change. As long as we have committed to the silent syntax, why not go the full nine yards!

[Niklas Kurz]

What a hoot! Just one thing: what does

.'

stand for?

[Bruno Luong]

Click on .'