Ring detail

Name: Nakayama's quasi-Frobenius ring that isn't Frobenius

Description: Let $k$ be the field of two elements, and consider the subring of matrices of the form $\begin{bmatrix}a&b&p&0&0&0\\c&d&q&0&0&0\\0&0&r&0&0&0\\0&0&0&r&s&t\\0&0&0&0&a&b\\0&0&0&0&c&d\end{bmatrix}$ with entries in $k$.

Notes: Jacobson radical is the subset with $a=b=c=d=r=0$.

Krull dimension: 0

Keywords matrix ring subring


  • T. Nakayama. On Frobeniusean algebras. I. (1939) @ pp 61-633
  • T.-Y. Lam. Lectures on modules and rings. (2012) @ Example 16.19(5) p 429