
R = [ 1  0 -1  1 1  ;
      0  0  1  2 3 ;
      0  0  0 -1 4 ;
      0  0  0  0 0 ;
      0  0  0  0 1 ]

%% rank(R) = 4 

S = [ 1  0 -1  1 1  ;
      0  2  1  2 3 ;
      0  0 -1 -1 4 ;
      0  0  0  0 0 ;
      0  0  0  0 0  ] 

%% rank(S) = 3
