Question

Determine the nature of the system: y(n)=x(-n).

(a) Causal

(b) Non-causal

(c) Causal for all positive values of n

(d) Non-causal for negative values of n

I had been asked this question during an interview for a job.

I would like to ask this question from Properties of Systems topic in portion Signals and Systems Basics of Signals and Systems

Answer 1

Right answer is (b) Non-causal

For explanation: The given system gives negative values of input i.e., past values of input when we feed positive integers to LHS. However, it gives positive values for negative values of n i.e., future values. Therefore, the system depends upon past values for some integers and future values for some other. A system cannot be called partially causal or non-causal, therefore, the system is non-causal.