(12)  W  = A  ⋅ M  = a  1     a  2     ⋮   a  N         T    m  11    m  12    ⋯   m  1 j     m  21    m  22    ⋯   m  2 j     ⋮  ⋮  ⋱  ⋮   m  N 1    m  N 2    ⋯   m  N j