Causal system
In control theory, a causal system (also known as a physical or nonanticipative system) is a system where the output depends on past and current inputs but not future inputs—i.e., the output y ( t 0 ) {\displaystyle y(t_{0})} depends only on the input x ( t ) {\displaystyle x(t)} for values of t ≤ t 0 {\displaystyle t\leq t_{0}} . The idea that the output of a function at any time depends only on past and present values of input is defined by the property commonly referred to as causality.