n = {-5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5};
   nn = {-5, -4, -3, -2, -1, 0, 1};
   mm = {2, 3, 4, 5};
   a = A*E^(I*k*nn) + B*E^(-I*k*nn) %for n<=1
   b = T*E^(I*k*mm)                 %for n>=2