7. Probability

Main references for this chapter include [36, 55, 64, 68, 69, 72].

The step function and sign function relation:

\[ u(t) = \frac{1}{2} [1 + \sgn (t)]. \]

Discrete step function and Kronecker delta function:

\[ u(n) = \sum_{k = -\infty}^n \delta(k). \]