Causality

Learned from MATH213.

Definition 2: Causality

A system A is causal if $y(t)=(Sf)(t)$ only depends on $f(\tau )$ for $\tau \le t$.

Definition 3: Causality (Alternate Definition)

A system $A$ is causal if for all $t\ge 0$ whenever $f_1(\tau )=f_2(\tau )$ for all $\tau \le t$ and $y_1(t)=(S{f}_1)(t)$ and $y_2(t)=(S{f}_2)(t)$ then $y_1(\tau )=y2(\tau )$, for all $\tau \le t$.