华东师范大学学报(自然科学版) ›› 2016, Vol. 2016 ›› Issue (2): 30-34.doi: 2016.02.004
交换$C^*$-代数有许多特征. 在本文中,证明了~$C^*$-代数~$\mathcal{A}$~是非交换的当且仅当其包络 冯诺依曼代数~$\mathcal{A}''$~中有一个~$C^*$-子代数~$\mathcal{B}$, $\mathcal{B}$~$*$-同构于2阶矩阵代数~$\mathrm M_2(\C)$. 基于这个性质,又可以得到一些旧命题的新证明方法.
There are many characterizations for commutative C^*-algebras. In this note, we prove that a C^*-algebra \mathcal{A} is not commutative if and only if there is a C^*-subalgebra \mathcal{B} in \mathcal{A}'' (the enveloping Von Neumann algebra of mathcal{A}) such that mathcal{B} is -isomorphic to \mathrm M_2(\mathcal{\textbf{C}}). In terms of this result, we can recover some characterizations for the commutativity of C^*-algebras appeared before