Question

A system is said to be causal if the output of the system depends on ___________

(a) The Past and Present Inputs

(b) The Present Inputs

(c) The Future Inputs

(d) The Past and Future Inputs

I had been asked this question by my college director while I was bunking the class.

Origin of the question is Fourier Series and LTI Systems topic in section Fourier Series of Signals and Systems

Answer 1

The correct option is (a) The Past and Present Inputs

Easiest explanation: A system is causal if and only if the current output is only a function of present and past inputs. The current output does not depend on the future inputs y (k) = f(u(k)); u(k-1); u(k-2);).