function env = envelope(A)
% Calculate the envelope of a matrix A
% Assume that A is symmetric.
  
  [m,n] = size(A);
  env = 0;
  
  for k = 2:n
    v = A(k,1:k-1);
    t = min(find(v));
    if (t > 0)
      env = env + (k-t);
    end
  end