The Kadison-Singer problem for the direct sum of matrix algebras

Charles Akemann, Joel Anderson, Betul Tanbay

Let $M_n$ denote the algebra of complex $n\times n$ matrices and write $M$ for the direct sum of the $M_n$. So a typical element of $M$ has the form \[x = x_1\oplus x_2 \... \oplu…