Dynamic Principal Components in the Time Domain
  We propose a time domain approach to define dynamic principal components (DPC) using a reconstruction of the original series criterion. This approach to define DPC was introduced by Brillinger, who gave a very elegant theoretical solution in the stationary case using the cross spectrum. Our procedure can be applied under more general conditions including the case ofnon stationary series and relatively short series. We also present a robust version of our procedure that allows to estimate the DPC when the series have outlier contamination. Our non robust and robust procedures are illustrated with real datasets. 
Daniel Pe\~na and V\'ictor J. Yohai
math.ST stat.TH