Definition:Unitary Matrix

Definition
Let $\mathbf U$ be a square matrix.

Then $\mathbf U$ is unitary :
 * $\mathbf U^{-1} = \mathbf U^\dagger$

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