how to create a 3D cone ?

i am trying like this

m=1000;
n=1000;
r=2;
h=5;
for i=1:m
    for j=1:n
        I(i,j)=1/3*pi*r^2*h*i/n;
    end
end
imshow(I)

but i am not getting result,please help

Answer 1

[KSSV]

r = linspace(0,2*pi) ;
th = linspace(0,2*pi) ;
[R,T] = meshgrid(r,th) ;
X = R.*cos(T) ;
Y = R.*sin(T) ;
Z = R ;
surf(X,Y,Z)

[ajeet verma]

i need base on the bottom and peaks on the top

[KSSV]

r = -linspace(0,2*pi) ;
th = linspace(0,2*pi) ;
[R,T] = meshgrid(r,th) ;
X = R.*cos(T) ;
Y = R.*sin(T) ;
Z = R ;
surf(X,Y,Z)

[ajeet verma]

thankyou

[Alexandr Cizek]

How would I get one with defined radius and height?