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