function A = blocks(n,m)

A(1:n,1:m) = 0;
A(n+1:2*n,m+1:2*m) = 0;
A(1:n,m+1:2*m) = 1;
A(n+1:2*n,1:m) = 1;

return;
A = [zeros(n,m) ones(n,m); ones(n,m) zeros(n,m)];

