单位样值序列¶

\[ \delta(k) := \left\{\begin{matrix} 1, &k=0 \\ 0, &k\neq0 \end{matrix}\right. \]

\[ f(k)\delta(k)=f(0)\delta(k) \]

\[ f(k)\delta(k-k_0)=f(k_0)\delta(k-k_0) \]

\[ \sum_{k=-\infty}^{+\infty}f(k)\delta(k)=f(0) \]

\[ \delta(k)=\varepsilon(k)-\varepsilon(k-1) \]