Z変換
f ( ∞ ) = lim k → ∞ f ( k ) = lim z → 1 { z − 1 z F ( z ) } {\displaystyle f(\infty )=\lim _{k\to \infty }f(k)=\lim _{z\to 1}\left\{{\frac {z-1}{z}}F(z)\right\}}