function [co] = comatrix( n)
%  builds the matrix C, see formula 2.37 os SISC article
for i=2:n
    delta(i)=sqrt(2./n);
end
delta(1)=sqrt(1./n);
for i=1:n
    for j=1:n
        co(i,j)=delta(i)*cos((i-1)*(2*j-1)*pi/(2*n));
    end
end
end

