Clean matrices and unit-regular matrices |
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Authors: | Dinesh Khurana T.Y. Lam |
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Affiliation: | aDepartment of Mathematics, Panjab University, Chandigarh-160014, India;bDepartment of Mathematics, University of California, Berkeley, CA 94720, USA |
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Abstract: | An element in a ring R is said to be clean (respectively unit-regular) if it is the sum (respectively product) of an idempotent element and an invertible element. If all elements in R are unit-regular, it is known that all elements in R are clean. In this note, we show that a single unit-regular element in a ring need not be clean. More generally, a criterion is given for a matrix to be clean in a matrix ring M2(K) over any commutative ring K. For K=Z, this criterion shows, for instance, that the unit-regular matrix is not clean. Also, this turns out to be the “smallest” such example. |
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