From 3a8106e4d03d3d5133ea6291e72826ef92ade398 Mon Sep 17 00:00:00 2001 From: Bokuan Li Date: Wed, 14 Oct 2026 20:04:57 -0400 Subject: [PATCH] Upgraded Kadison-Schwarz. --- src/op/system/completely.tex | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/src/op/system/completely.tex b/src/op/system/completely.tex index 93b323c..d9056b2 100644 --- a/src/op/system/completely.tex +++ b/src/op/system/completely.tex @@ -111,38 +111,43 @@ \begin{proposition}[Kadison-Schwarz Inequality] \label{proposition:cauchy-schwarz-2-positive} - Let $A, B$ be unital $C^*$-algebras, $\phi: A \to B$ be a unital $2$-positive map, then for each $x \in A$, + Let $A, B$ be unital $C^*$-algebras, $\phi: A \to B$ be a $2$-positive map, then for each $x \in A$, \[ - \phi(x)^*\phi(x) \le \phi(x^*x) + \phi(x)^*\phi(x) \le \norm{\phi(1_A)}_B \phi(x^*x) \] + + xxx \end{proposition} \begin{proof} Since \[ \begin{bmatrix} - 1 &x \\ + 1_A &x \\ x^* &x^*x \end{bmatrix} = \begin{bmatrix} - 1 &x \\ + 1_A &x \\ 0 &0 \end{bmatrix}^*\begin{bmatrix} - 1 &x \\ + 1_A &x \\ 0 &0 \end{bmatrix} \ge 0 \] - and $\phi$ is unital and $2$-positive, + and $\phi$ is $2$-positive, \[ \begin{bmatrix} - 1 &\phi(x) \\ + 1_B\norm{\phi(1_A)}_B &\phi(x) \\ + \phi(x)^* &\phi(x^*x) + \end{bmatrix} \ge \begin{bmatrix} + \phi(1_A) &\phi(x) \\ \phi(x)^* &\phi(x^*x) \end{bmatrix} = \phi_2\begin{bmatrix} - 1 &x \\ + 1_A &x \\ x^* &x^*x \end{bmatrix} \ge 0 \] - By \autoref{lemma:norm-matrix-test}, $\phi(x)^*\phi(x) \le \phi(x^*x)$. + By \autoref{lemma:norm-matrix-test}, $\phi(x)^*\phi(x) \le \norm{\phi(1_A)}_B\phi(x^*x)$. \end{proof}