Using representation-theoretic methods. we determine the spectrum of the 2
x 2 system
Q(x, D-x) = A(-partial derivative (2)(x)/2 + x(2)/2) + B(x partial derivati
ve (x) + 1/2), x is an element of R,
with A, B is an element of Mat(2)(R) constant matrices such that A = (t)A >
0 (or <0), B = -B-t <not equal> 0, and the Hermitian matrix A + iB positiv
e (or negative) definite. We also give results that generalize (in a possib
le direction) the main construction.