Problem with drawing a hyperboloid

Hello,

I wrote the following code:

r=linspace(-3,3,21);
theta=linspace(0,2*pi,63);
m = 1

[R,THETA]=meshgrid(r,theta);
X=R.*cos(THETA);
Y=R.*sin(THETA);
Z = R;
C = (X.^2 + Y.^2 - Z.^2).^m;

surf(X,Y,Z,C) 
axis equal
colormap jet

It becomes a cone-like hyperboloid instead, and I can not figure out where I am getting it wrong.

Any help is appreciated!

Thanks in advance.

Answer 1

[DGM]

You get a simple bicone because

Z = R;

and the colormapping looks random because

C = (X.^2 + Y.^2 - Z.^2).^m; 

is essentially zero (it's just a collection of rounding errors, really), since

Z^2 = R^2
R^2 = X^2+Y^2

I'm not really sure what you're intending, but that's why you're getting what you get.