Here we go
r = 1;
R = 2; % must be > r
h = 3;
if R <= r
error('Non valid parameter')
end
Zmin = r*h/(R-r); % Position where the frustrum starts
Zmax = R*h/(R-r); % Position where the frustrum ends
N = 1e4; % Number of point
zr = (Zmin/Zmax).^3;
z = (zr + (1-zr)*rand(1,N)).^(1/3);
rho = R*sqrt(rand(1,N)).*z;
theta = (2*pi)*rand(1,N);
x = rho.*cos(theta);
y = rho.*sin(theta);
z = Zmax*(1-z);
scatter3(x,y,z,'.');
axis equal
