# Definition:Unitary Matrix

## Definition

Let $\mathbf U$ be an invertible square matrix over $\C$.

Then $\mathbf U$ is unitary if and only if:

$\mathbf U^{-1} = \mathbf U^\dagger$

where:

$\mathbf U^{-1}$ is the inverse of $\mathbf U$
$\mathbf U^\dagger$ is the Hermitian conjugate of $\mathbf U$