function Apr24()
% Assume that m = 5, n = 3 and r = 2.
%
%                    s 0 0 
% If U'*A*V = Sig =  0 s 0
%                    0 0 0
%                    0 0 0
%                    0 0 0
% then
%                                          0  0  0  0  0  s  0  0
%                                          0  0  0  0  0  0  s  0
%       U'    0    0   A       U    0      0  0  0  0  0  0  0  0
%                *        *             =  0  0  0  0  0  0  0  0
%       0     V'   A'  0       0    V      0  0  0  0  0  0  0  0
%                                          s  0  0  0  0  0  0  0 
%                                          0  s  0  0  0  0  0  0
%                                          0  0  0  0  0  0  0  0
% Note that the columns of I(:,[3 4 5 8]) are in the nullspace of this.
% Thus, columns 3 4 5 and 8 of
%
%                  U  0
%                  0  V
% span the nullspace of B