Past exam of the mathematics course of the University of Cambridge / 2024 / ii / Paper 1 / 14D / a / Solution

A system is causal if outputs up to time $t$ depend only on inputs up to time $t$. For a time-invariant convolution system this is equivalent to an impulse response $g(t)$ that vanishes for $t<0$.

It is BIBO stable if every bounded input produces a bounded output. For a causal convolution system, absolute integrabilityis the standard stability criterion.