Question

Comment on the causality of the following discrete time system: y[n] = x[-n].

(a) Causal

(b) Non causal

(c) Both Casual and Non casual

(d) None of the mentioned

I got this question in semester exam.

My doubt stems from Discrete-Time Systems in the Time-Domain in section Signals and Systems Basics of Signals and Systems

Answer 1

The correct option is (b) Non causal

For explanation I would say: For positive time, the output depends on the input at an earlier time, giving causality for this portion. However, at a negative time, the output depends on the input at a positive time, i.e. at a time in the future, rendering it non causal.