References Brockwell, P. J., and R. A. Davis (1987): Time Series: Theory and Methods, Springer series in Statistics. Springer-Verlag, New York. Bujosa, M., A. Garc´ıa-Ferrer, and P. C. Young (2002): “An ARMA representation of unobserved component models under generalized random walk specifications: new algorithms and examples,”mimeo. Caines, P. E. (1988): Linear Stochastic Systems, Wiley series in probability and mathematical statistics. John Wiley & Sons, Inc., New York. Godement, R. (1974): ´ Algebra. Editorial Tecnos, Madrid, first edn. Harvey, A. (1989): Forecasting Structural Time Series Models and the Kalman Filter. Cambridge University Press, Cambridge, first edn. Hatanaka, M., and M. Suzuki (1967): “A theory of the Pseudosprectrum and Its Application to Nonstationary Dynamic Ecomometric Models,” in Essays in Mathematical Economics. In Honor of Oskar Morgenstern, ed. by M. Shubik, chap. 26, pp. 443–446. Princeton University Press, Princeton, New Jersey. Luenberger, D. G. (1968): Optimization by vector space methods, Series in decision and control. John Wiley & Sons, Inc., New York. Priestley, M. P. (1981): Spectral Analysis and Time Series, Probability and Mathematical Statistics. Academic Press, London, first edn. Young, P. C., D. Pedregal, and W. Tych (1999): “Dynamic Harmonic Regression,” Journal of Forecasting, 18, 369–394.