combination(m,n,r)

function c = combination(m,n,r)
%COMBINATION   Returns a nCr*r matrix C.
%   nCr represents the total number of different mothods of selecting r
%   numbers from m to n.
%
%   Copyright Phymhan Studio.
%   $Revision: 1.1 $  $Date: 2013/03/27 13:12:37 $
%
if nargin == 2
    r = n;
    n = m;
    m = 1;
end
c = comb_recs(m,n,r);
    function c = comb_recs(m,n,r)
        if (n-m+1) < r
            c = [];
            return;
        end
        if r == 1
            c = (m:n)';
            return;
        end
        nCr = factorial(n-m+1)/(factorial(r)*factorial(n-m+1-r));
        c = zeros(nCr,r);
        cstart = 1;
        for k = m:(n-r+1)
            Csub = combination((k+1),n,(r-1));
            cend = cstart+size(Csub,1)-1;
            c(cstart:cend,1) = k;
            c(cstart:cend,2:r) = Csub;
            cstart = cend+1;
        end
    end
end