function [H] = create_H_matrix(n)
% create the H matrix 
%
% Written by:
% -- 
% John L. Weatherwax                2009-04-21
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

H = zeros(2*n+1,n);
for ii=0:n
  H(2*ii+1,ii+1) = +1; 
  if( ii ~= n )
    H(2*(ii+1),ii+1) = -1; 
    H(2*(ii+1),ii+2) = +1; 
  end
end