Cellularity of centrosymmetric matrix algebras and Frobenius extensions

Centrosymmetric matrices of order $n$ over an arbitrary algebra $R$ form a subalgebra of the full $n\times n$ matrix algebra over $R$. It is called the centrosymmetric matrix algebra of order $n$ over $R$ and denoted by $S_n(R)$. We prove (1) $S_n(R)$ is Morita equivalent to $S_2(R)$ if $n$ is even, and to $S_3(R)$ if $n\ge 3$ is odd; (2) the full $n\times n$ matrix algebra over $R$ is a separable Frobenius extension of $S_n(R)$; and (3) if $R$ is a commutative ring, then $S_n(R)$ is a cellular $R$-algebra in the sense of Graham-Lehrer for all $n\ge 1$.

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