The spectra and pseudospectra of nonsymmetric Toeplitz or circulant
matrices with slowly varying coefficients are considered. Such matrices
are characterized by a symbol that depends on both space and wave
number. It is shown that when a certain twist condition is satisfied,
analogous to Hormander's commutator condition for partial differential
equations, epsilon-pseudoeigenvectors of such matrices for exponentially
small values of epsilon exist in the form of localized wave packets.
These results are a discrete analogue of similar results for differential
operators discussed recently by E. B. Davies and M. Zworski.