Matrices over local rings: criteria for decomposability

Research output: Working paper/PreprintPreprint


Let (S, m) be a local ring over a field (the simplest example is analytic/formal
power series). Consider matrices with entries in S, up to left-right equivalence, A → UAV , where U, V are invertible matrices over S. When such a matrix is equivalent to a block-diagonal matrix? Alternatively, when the S-module coker(A) is decomposable?
An obvious necessary condition (for square matrices) is that the determinant of the matrixis reducible (as an element of S). This condition is very far from being sufficient. We prove a very simple necessary and sufficient condition for equivalence to block-diagonal form.
As immediate applications we prove several results: the Ulrich modules over local rings tend to be decomposable; an obstruction to Thom-Sebastiani decomposability of maps (or of systems of vector fields/PDE’s); decomposable representations of algebras are avoidable in projective families; decomposable matrices are highly unstable (they are far from being finitely
determined); etc..
Original languageEnglish
StatePublished - 10 May 2013

Publication series

NamearXiv preprint


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