span(A₁, . . . ,An) denotes the linear space spanned by Hilbert space operators A₁, . . . ,An. It is known that if span (A, B) consists of normal operators, then A, B commute. Let MI denote the set of ...

This paper reviews and extends several aspects of the analysis of linear combinations of time series. Special cases are temporal and contemporaneous aggregations and systematic sampling. We present ...