7. Probability

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

The step function and sign function relation:

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

Discrete step function and Kronecker delta function:

$$u(n)=\sum _{k=-\mathrm{\infty }}^n\delta (k).$$