Identity Matrix

Definition

A square matrix with $1$‘s on the main diagonal and $0$‘s elsewhere is called an identity matrix.

Usually denoted as $I$, or if the sizes are important, $I_n$.

Example

$$\left[\begin{array}{c}1\end{array}\right],\left[\begin{array}{cc}1& 0\\ 0& 1\end{array}\right],\left[\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\\ 0& 0& 1\end{array}\right]$$