A causal system is a system whose output at any time depends only on input values at that time and earlier times, not on future input values. For a continuous-time
linear time-invariant system, causality
is equivalent to its impulse response function
satisfying 
for 
. For a discrete-time linear
time-invariant system, the corresponding condition is 
for 
.
Causal System
See also
Convolution, Impulse Response Function, Linear Time-Invariant SystemExplore with Wolfram|Alpha
References
Oppenheim, A. V.; Willsky, A. S.; and Nawab, S. H. Signals and Systems, 2nd ed. Upper Saddle River, NJ: Prentice Hall, 1997.Cite this as:
Weisstein, Eric W. "Causal System." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CausalSystem.html