Let x, ybe two Hermitian matrices on Cn. Define u =e2πinx, v =e2πiny. We use Mnto denote the algebra of all n ×ncomplex matrices generated by Uand Vwith the bracket [u, v] =uv −vu. Then CI, which is the scalar multiple of the identity matrices I, is the commutator of the operation [u, v]. Sometimes we simply use 1to denote the n ×nidentity matrix