Inner automorphisms #
This file defines the inner automorphism of a unitary matrix U
as U x U⁻¹
and proves that any star-algebraic automorphism on Mₙ(ℂ)
is an inner automorphism.
Equations
- unitary.inner_aut_star_alg K a = let _inst : invertible ↑a := {inv_of := has_star.star ↑a, inv_of_mul_self := _, mul_inv_of_self := _} in star_alg_equiv.of_alg_equiv (algebra.aut_inner ↑a) _
given a unitary $U$, we have the inner algebraic automorphism, given by $x \mapsto UxU^*$ with its inverse given by $x \mapsto U^* x U$
Equations
inner automorphism (matrix.inner_aut_star_alg
), but as a linear map
Equations
the spectrum of $U x U^*$ for any unitary $U$ is equal to the spectrum of $x$
the spectrum of a linear map $x$ equals the spectrum of
$f_U^{-1} x f_U$ for some unitary $U$ and $f_U$ is
the inner automorphism (matrix.inner_aut
)
the inner automorphism is unital
the trace of $f_U(x)$ is equal to the trace of $x$
$x$ is Hermitian if and only if $f_U(x)$ is Hermitian
$f_U(x)$ is positive definite if and only if $x$ is positive definite
Schur decomposition, but only for almost Hermitian matrices: given an almost Hermitian matrix $A$, there exists a diagonal matrix $D$ and a unitary matrix $U$ such that $UDU^*=A$
any $^*$-isomorphism on $M_n$ is an inner automorphism
Equations
- matrix.star_alg_equiv.unitary f = (λ (_x : matrix.inner_aut_star_alg (classical.some _) = f), classical.some _) _
Equations
- matrix.unitary_group.conj U = ⟨matrix.conj ⇑U, _⟩
Equations
- matrix.unitary_group.kronecker U₁ U₂ = ⟨matrix.kronecker_map has_mul.mul ⇑U₁ ⇑U₂, _⟩