Trouble Understanding Code for a Hemisphere

I have used the following code to create a hemisphere with radius 10. Unfortunately I don't really understand what the code does, so if someone could explain this that would be great. Please try to be as detailed as possible, thanks.

figure (1)
[x,y,z]=sphere;

x=x(11:end,:);

y=y(11:end,:);

z=z(11:end,:);

r=10;

hemisphere=surf(r.*x,r.*y,r.*z);
axis equal

Answer 1

[Walter Roberson]

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

"sphere generates a sphere consisting of 20-by-20 faces."

so accessing the coordinates from 11 onwards would be only half of a sphere.

"The sphere function generates the x-, y-, and z-coordinates of a unit sphere for use with surf and mesh."

If you multiply coordinates based on the unit sphere by the radius of the sphere, then you get a sphere of that radius.

Then you draw the surface. After that you tell MATLAB that you want the x, y, and z axes to be the same spacing as each other (the default is to stretch the data to whatever the current size of the axes is.)

[Jonathan Bird]

Thanks! really helpful

[Jonathan Bird]

Please could you explain what ",:"means in "11:end,:" ?

[Walter Roberson]

: by itself means the same as 1:end which in turn means the same as 1 : size(TheArray,AppropriateDimensionNumber) .

In short, : by itself in that context means "all columns"