Identity matrix
A square matrix with \(1\)s on its main diagonal and \(0\)s elsewhere,
\begin{equation*} I_n = \begin{pmatrix} 1 & 0 & \cdots & 0 \\ 0 & 1 & \cdots & 0 \\ \vdots & \vdots & \ddots & \vdots \\ 0 & 0 & \cdots & 1 \end{pmatrix}. \end{equation*}