In this paper, we first consider n × n upper-triangular matrices with entries in a given semiring k. Matrices of this form with invertible diagonal entries form a monoid Bn(k). We show that Bn(k) splits as a semidirect product of the monoid of unitriangular matrices Un(k) by the group of diagonal matrices. When the semiring is a field, Bn(k) is actually a group and we recover a well-known resul...

A class of finite semigroups V is said to be decidable if the membership problem for V has a solution, that is, if we can construct an algorithm to test whether a given semigroup lies in V. Decidability of pseudovarieties is not preserved by some of the most common pseudovariety operators, such as semidirect product, Mal’cev product and join [1, 17]. In particular Rhodes [17] has exhibited a de...

We present an efficient quantum algorithm for the hidden subgroup problem (HSP) on the semidirect product of cyclic groups Zpr oφ Zps , where p is any odd prime number and r and s are any positives integers such that r ≥ 2s. This quantum algorithm is exponentially more efficient than any classical algorithm for the same purpose. Resumo. Neste trabalho, apresentamos um algoritmo quântico eficien...

Abstract. The multiplier representation of the generalized symmetry group of a quasiperiodic flow on the n-torus defines, for each subgroup of the multiplier group of the flow, a group invariant of the smooth conjugacy class of that flow. This group invariant is the internal semidirect product of a subgroup isomorphic to the n-torus by a subgroup isomorphic to that subgroup of the multiplier gr...

Let G be a group which admits the structure of an iterated semidirect product of finitely generated free groups. We construct a finite, free resolution of the integers over the group ring of G. This resolution is used to define representations of groups which act compatibly on G, generalizing classical constructions of Magnus, Burau, and Gassner. Our construction also yields algorithms for comp...

The q-Poincaré group of [1] is shown to have the structure of a semidirect product and coproduct B>⊳ ̃ SOq(1, 3) where B is a braided-quantum group structure on the q-Minkowski space of 4-momentum with braided-coproduct ∆p = p⊗ 1+1⊗p. Here the necessary B is not a usual kind of quantum group, but one with braid statistics. Similar braided-vectors and covectors V (R), V (R) exist for a general R...

Let N be a simply connected nilpotent Lie group and let S = N o (R+)d be a semidirect product, (R+)d acting on N by diagonal automorphisms. Let (Qn, Mn) be a sequence of i.i.d. random variables with values in S. Under natural conditions, including contractivity in the mean, there is a unique stationary measure ν on N for the Markov process Xn = MnXn−1 + Qn. We prove that for an appropriate homo...

We associate the iterated block product of a bimachine with a deterministic Turing machine. This allows us to introduce new algebraic notions to study the behavior of the Turing machine. Namely, we introduce double semidirect products through matrix multiplication of upper triangular matrices with coefficients in certain semigroups, which leads in turn to the study of the iterations of bimachin...

Giuseppe Gaeta Centre de Physique Th eorique, Ecole Polytechnique F 91128 Palaiseau (France) and Departamento de Fisica Teorica II, Universidad Complutense E 28040 Madrid (Spain) Summary. We prove that any dynamical system on a G-manifold M which is equivariant under the G action, can be decomposed into the semidirect product of an autonomous dynamics in the G-orbit space = M=G, and a dynamics ...

In this paper we characterize the congruence associated to the direct sum of all irreducible representations of a finite semigroup over an arbitrary field, generalizing results of Rhodes for the field of complex numbers. Applications are given to obtain many new results, as well as easier proofs of several results in the literature, involving: triangularizability of finite semigroups; which sem...