  The implicitly shifted QR iteration is used as a restart procedure for the
Arnoldi method for the calculation of a few dominant eigenvalues of a large
matrix. We show that the underlying idea of implicit polynomial filtering can
be utilized in much the same manner via the implicitly shifted LR iteration to
create a restart procedure for the non-symmetric Lanczos algorithm for
eigenvalue computations, which preserves the tri-diagonal structure of the
reduced matrix.
