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EXT-FINITE MODULES FOR WEAKLY SYMMETRIC ALGEBRAS WITH RADICAL CUBE ZERO

Part of: Basic linear algebra Representation theory of rings and algebras Homological methods

Published online by Cambridge University Press:  19 September 2016

KARIN ERDMANN
KARIN ERDMANN*
Affiliation:
Mathematical Institute, University of Oxford, ROQ, Oxford OX2 6GG, UK email [email protected]
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Abstract

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Assume that $A$ is a finite-dimensional algebra over some field, and assume that $A$ is weakly symmetric and indecomposable, with radical cube zero and radical square nonzero. We show that such an algebra of wild representation type does not have a nonprojective module $M$ whose ext-algebra is finite dimensional. This gives a complete classification of weakly symmetric indecomposable algebras which have a nonprojective module whose ext-algebra is finite dimensional. This shows in particular that existence of ext-finite nonprojective modules is not equivalent with the failure of the finite generation condition (Fg), which ensures that modules have support varieties.

Keywords

extensionsfinite global dimensionweakly symmetric algebrasChebyshev polynomials

MSC classification

Primary: 16E40: (Co)homology of rings and algebras (e.g. Hochschild, cyclic, dihedral, etc.) 16G10: Representations of Artinian rings
Secondary: 16E05: Syzygies, resolutions, complexes 15A24: Matrix equations and identities 33C45: Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.)
Type
Research Article
Information
Journal of the Australian Mathematical Society , Volume 102 , Issue 1 , February 2017 , pp. 108 - 121
Copyright
© 2016 Australian Mathematical Publishing Association Inc. 

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