Notations and Symbols Basic Notations R, C, Z j x z -1 d dt x(t), real/complex/integer numbers -1 complex conjugation unit delay x (t) differentiation/derivative inner product x, x 2 x, y x = norm energy continuous-time convolution discrete-time convolution real part, imaginary part space of square-integrable functions on R space of square-summable functions on Z definition E x = x (x y)(t) (x y)[n] Re{·}, Im{·} L 2 (R) l 2 (Z)