1,523 research outputs found
Locally finite derivations and modular coinvariants
We consider a finite dimensional kG-module V of a p-group G over a field k of characteristic p. We describe a generating set for the corresponding Hilbert Ideal. In case G is cyclic this yields that the algebra k[V]_G of coinvari-ants is a free module over its subalgebra generated by kG-module generators of V^∗ . This subalgebra is a quotient of a polynomial ring by pure powers of its variables. The coinvariant ring was known to have this property only when G was cyclic of prime order. In addition, we show that if G is the Klein 4-group and V does not contain an indecomposable summand isomorphic to the regular module, then the Hilbert Ideal is a complete intersection, extending a result of the second author and R. J. Shank
Coinvariants and the regular representation of a cyclic P-group
Cataloged from PDF version of article.We consider an indecomposable representation of a cyclic p-group Zpr over a field of characteristic p. We show that the top degree of the corresponding ring of coinvariants is less than. This bound also applies to the degrees of the generators for the invariant ring of the regular representation. © 2012 Springer-Verlag
Explicit separating invariants for cyclic p-groups
Cataloged from PDF version of article.We consider a finite-dimensional indecomposable modular representation of a cyclic p-group and we give a recursive description of an associated separating set: We show that a separating set for a representation can be obtained by adding, to a separating set for any subrepresentation, some explicitly defined invariant polynomials. Meanwhile, an explicit generating set for the invariant ring is known only in a handful of cases for these representations. © 2010 Elsevier Inc. All rights reserved
Constructing modular separating invariants
Cataloged from PDF version of article.We consider a finite dimensional modular representation V of a cyclic group of prime order p. We show that two points in V that are in different orbits can be separated by a homogeneous invariant polynomial that has degree one or p and that involves variables from at most two summands in the dual representation. Simultaneously, we describe an explicit construction for a separating set consisting of polynomials with these properties. (C) 2009 Elsevier Inc. All rights reserved
Degree bounds for modular covariants
Let V,W be representations of a cyclic group G of prime order p over a field k of characteristic p. The module of covariants k[V,W]^G is the set of G-equivariant polynomial maps from V to W, and is a module over the algebra of invariants k[V]^G. We give a formula for the Noether bound of k[V,W]^G over k[V]^G, i.e. the minimal degree d such that k[V,W]^G is generated over k[V]^G by elements of degree at most d
Separating Invariants for the Klein Four Group and Cyclic Groups
Cataloged from PDF version of article.We consider indecomposable representations of the Klein four group over a field of characteristic 2 and of a cyclic group of order pm with p, m coprime over a field of characteristic p. For each representation, we explicitly describe a separating set in the corresponding ring of invariants. Our construction is recursive and the separating sets we obtain consist of almost entirely orbit sums and products. © 2013 World Scientific Publishing Compan
On the top degree of coinvariants
Cataloged from PDF version of article.For a finite group G acting faithfully on a finite-dimensional F-vector space V, we show that in the modular case, the top degree of the vector coinvariants grows unboundedly: lim(m ->infinity) topdeg F[V-m](G) = infinity. In contrast, in the nonmodular case we identify a situation where the top degree of the vector coinvariants remains constant. Furthermore, we present a more elementary proof of Steinberg's theorem which says that the group order is a lower bound for the dimension of the coinvariants which is sharp if and only if the invariant ring is polynomial
Associative memory design using overlapping decompositions
Cataloged from PDF version of article.This paper discusses the use of decomposition techniques in the design of associative memories via arti"cial neural networks. In
particular, a disjoint decomposition which allows an independent design of lower-dimensional subnetworks and an overlapping
decomposition which allows subnetworks to share common parts, are analyzed. It is shown by a simple example that overlapping
decompositions may help in certain cases where design by disjoint decompositions fails. With this motivation, an algorithm is
provided to synthesize neural networks using the concept of overlapping decompositions. Applications of the proposed design
procedure to a benchmark example from the literature and to a pattern recognition problem indicate that it may improve the
e!ectiveness of the existing methods. ( 2001 Published by Elsevier Science Ltd
Separating invariants for arbitrary linear actions of the additive group
We consider an arbitrary representation of the additive group G_a
over a field of characteristic zero and give an explicit description of a finite separating set in the corresponding ring of invariants
Robust adaptive sampled-data control of a class of systems under structured nonlinear perturbations
Cataloged from PDF version of article.A robust adaptive sampled-data feedback stabilization
scheme is presented for a class of systems with nonlinear additive
perturbations. The proposed controller generates a control input by
using high-gain static or dynamic feedback from nonuniform sampled
values of the output. A simple adaptation rule adjusts the gain and the
sampling period of the controller
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