samer@4: function t=circulant(c)
samer@4: % circulant - Construct circulant matrix from first column
samer@4: %
samer@4: % circulant :: [[N]] -> [[N,N]].
samer@4: 
samer@4: m = length(c);
samer@4: c=c(:); 
samer@4: 
samer@4: x = [c(2:m) ; c(:)];                 % build vector of user data
samer@4: cidx = (0:m-1)';
samer@4: ridx = m:-1:1;
samer@4: t = cidx(:,ones(m,1)) + ridx(ones(m,1),:);  % Toeplitz subscripts
samer@4: t(:) = x(t);                                   % actual data
samer@4: 
samer@4: