Bull. Austral. Math. Soc. 72(2) pp.317--324, 2005.

Complementation of the Jacobson group in a matrix ring

David Dolžan

Received: 4th July, 2005

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Abstract

The Jacobson group of a ring R (denoted by $ \cJ $ = $ \cJ $(R)) is the normal subgroup of the group of units of R (denoted by G(R)) obtained by adding 1 to the Jacobson radical of R $ \bigl ($J(R)$ \bigr )$. Coleman and Easdown in 2000 showed that the Jacobson group is complemented in the group of units of any finite commutative ring and also in the group of units of a n×n matrix ring over integers modulo ps, when n = 2 and p = 2, 3, but it is not complemented when p$ \ge $5. In 2004 Wilcox showed that the answer is positive also for n = 3 and p = 2, and negative in all the remaining cases. In this paper we offer a different proof for Wilcox's results and also generalise the results to a matrix ring over an arbitrary finite commutative ring. We show this by studying the generators and relations that define a matrix ring over a field. We then proceed to examine the complementation of the Jacobson group in the matrix rings over graded rings and prove that complementation depends only on the 0-th grade.

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(Metadata: XML, RSS, BibTeX) MathSciNet: MR2183412 Z'blatt-MATH: 02246393

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