Causal

  • A system is causal if for every x[n], y[n] at any n is not affected by x[m] where \(m>n\)
  • In other words, for DT systems, to find a non-causal system's output would requires knowing input values which are in the future.

Memoryless

  • A system is memoryless if for every x[n], y[n] at any n is not affected by x[m] where \(m<n\)
  • In other words, for DT Causal systems, to find a memoryless system's output would only require knowing the input at that point.

Things do not happen. Things are made to happen.
— John F. Kennedy