Definition:Unitary Matrix

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

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 $\mathbf U$

Also see

 * Definition:Unitary Group
 * Definition:Unitary Operator
 * Definition:Hermitian Matrix
 * Definition:Orthogonal Matrix