function out = torus(nbr,rad1,rad2);
% The function
% 
%       out = torus(nbr,revo,step);
% 
% generates a 3-dimensional database with <nbr> elements. 
% These elements draw a hollow torus. 
% The optional parameter <rad1> gives the main radius of 
% the torus; default value is 0.75. 
% The optional parameter <rad2> sets the second radius; 
% default value is 0.25.  

if nargin<3, rad2 = 0.25; end;
if nargin<2, rad1 = 0.75; end;

r = 2*pi*rand(nbr,1);
s = 2*pi*rand(nbr,1);

out = [(rad1+rad2*cos(s)).*cos(r), (rad1+rad2*cos(s)).*sin(r), rad2*sin(s)];