Definition:  complex quantity $s=\sigma +\mathrm{j}\omega$ associated with a quantity represented by $a(t)={A}_{0}{\mathrm{e}}^{\sigma \text{\hspace{0.05em}}t}\text{cos}(\omega \text{\hspace{0.05em}}t+{\vartheta}_{0})$, where $A}_{0$ is the initial amplitude, ω is the angular frequency, t is time, and ${\vartheta}_{0}$ is initial phase
