Intrinsic difficulties in using the doubly-infinite time axis for input-output systems theory.

T.T. Georgiou and M.C. Smith


We point out that the natural definitions of stability and causality in input-output systems theory lead to certain inconsistencies when inputs and outputs are allowed to have support on the doubly-infinite time-axis. In contrast, the use of the semi-infinite time axis gives a framework which appears to be more satisfactory to the intuition.