On the codimensions of the verbally prime P.I. algebras

Razmyslov’s theory of trace identities for the prime P.I. algebrasM _{k, l} is applied to give bounds for the cocharacters and the codimensions of these algebrasM _{k, l}, as well as for the matrix algebrasM _k(E) over the Grassmann algebraE. These bounds are easier to obtain and are better (tighter) than earlier obtained bounds. Work supported by NSF grant DMS 9100258. Work supported by NSF grant DMS 9101488.     

Asymptotic behaviour of codimensions of p. i. algebras satisfying Capelli identities

Let be a p. i. algebra with 1 in characteristic zero, satisfying a Capelli identity. Then the cocharacter sequence is asymptotic to a function of the form , where and .

     

Growth of codimensions of metabelian algebras

Numerical invariants of identities of nonassociative algebras are considered. It is proved that the codimension sequence of any finitely generated metabelian algebra has an exponentially bounded codimension growth. It is shown that the upper PI-exponent increases at most by 1 after adjoining an external unit. It is proved that for two-step left-nilpotent algebras the lower PI-exponent increases at least by 1.     

A characterization of algebras with polynomial growth of the codimensions

Let be an associative algebras over a field of characteristic zero. We prove that the codimensions of are polynomially bounded if and only if any finite dimensional algebra with has an explicit decomposition into suitable subalgebras; we also give a decomposition of the -th cocharacter of into suitable -characters.

We give similar characterizations of finite dimensional algebras with involution whose -codimension sequence is polynomially bounded. In this case we exploit the representation theory of the hyperoctahedral group.

     

Asymptotic growth of codimensions of identities of associative algebras

Numerical characteristics of identities of associative and non-associative algebras are studied in the paper. It is announced that the sequence of codimensions of an arbitrary associative PI-algebra asymptotically increases and that this is not true in the general non-associative case.     

Exact borel subalgebras of quasi-hereditary algebras,I

with an appendix by Leonard Scott     

On the asymptotic behaviour of some new gradient methods

The Barzilai-Borwein (BB) gradient method, and some other new gradient methods have shown themselves to be competitive with conjugate gradient methods for solving large dimension nonlinear unconstrained optimization problems. Little is known about the asymptotic behaviour, even when applied to n−dimensional quadratic functions, except in the case that n=2. We show in the quadratic case how it is possible to compute this asymptotic behaviour, and observe that as n increases there is a transition from superlinear to linear convergence at some value of n≥4, depending on the method. By neglecting certain terms in the recurrence relations we define simplified versions of the methods, which are able to predict this transition. The simplified methods also predict that for larger values of n, the eigencomponents of the gradient vectors converge in modulus to a common value, which is a similar to a property observed to hold in the real methods. Some unusual and interesting recurrence relations are analysed in the course of the study.This work was supported by the EPRSC in UK (no. GR/R87208/01) and the Chinese NSF grant (no. 10171104)     

Lie,Jordan and proper codimensions of associative algebras

We study the exponential rate of growth of the sequence of proper, Lie and Jordan codimensions of an associative algebra. We show that for any finite dimensional associative algebra, the exponential rates of growth can be explicitly computed and are strictly related to the PI-exponent of the algebra. The first author was partially supported by MIUR of Italy. The second author was partially supported by RFBR grant No 06-01-00485 and SSC-5666.2006.1     

Exact and asymptotic estimates forn-widths of some classes of periodic functions

Let \(\tilde W_p^r : = \left\{ {f\left| {f \in C^{r - 1} } \right.} \right.\left[ {0,2\pi } \right],f^{(i)} (0) = f^{(i)} (2\pi ),i = 0, \ldots ,r - 1,f^{(r - 1)}\) , abs. cont. on [0, 2π] andf ^(r)∈L ^p[0, 2π]}, and set \(\tilde B_p^r : = \left\{ {f\left| {f \in \tilde W_p^r ,} \right.\left\| {f^{(r)} } \right\|_p \leqslant 1} \right\}\) . We find the exact Kolmogrov, Gel'fand, and linearn-widths of \(\tilde B_p^r\) inL ^p forn even and allp∈(1, ∞). The strong asymptotic estimates forn-widths of \(\tilde B_p^r\) inL ^p are also obtained.     

Bases for some reciprocity algebras I

For a complex vector space , let be the algebra of polynomial functions on . In this paper, we construct bases for the algebra of all highest weight vectors in , where and for all , and the algebra of highest weight vectors in .

     

Exact borel subalgebras of quasi-hereditary algebras. II

In this article, we consider the class of flat G-modules in the category of discrete modules over a profinite group G. We will appeal to a recent result of Enochs to prove that we have flat covers in this situation.     

The analytic continuation and the asymptotic behaviour of certain multiple zeta-functions I

We consider general multiple zeta-functions of multi-variables, including both Barnes multiple zeta-functions and Euler-Zagier sums as special cases. We prove the meromorphic continuation to the whole space, asymptotic expansions, and upper bound estimates. These results are expected to have applications to some arithmetical L-functions (such as of Hecke and of Shintani). The method is based on the classical Mellin-Barnes integral formula.     

Automorphically rigid group algebras. I. Semisimple algebras

Classes of automorphically rigid semisimple group algebras KG are defined over finite fields K and finite groups G.     

Alternative approaches to asymptotic behaviour of eigenvalues of some unbounded Jacobi matrices

In this article we calculate the asymptotic behaviour of the point spectrum for some special self-adjoint unbounded Jacobi operators J   acting in the Hilbert space l²=l²(N)$l^2=l^2(\mathbb{N})$. For given sequences of positive numbers _λn${\lambda }_n$ and real _qn$q_n$ the Jacobi operator is given by J=SW+WS^*+Q$J=\text{<italic>SW</italic>}+{\mathit{WS}}^{*}+Q$, where Q=diag(_qn)$Q=\mathrm{diag}(q_n)$ and W=diag(_λn)$W=\mathrm{diag}({\lambda }_n)$ are diagonal operators, S is the shift operator and the operator J   acts on the maximal domain. We consider a few types of the sequences {_qn}$\{q_n\}$ and {_λn}$\{{\lambda }_n\}$ and present three different approaches to the problem of the asymptotics of eigenvalues of various classes of J's. In the first approach to asymptotic behaviour of eigenvalues we use a method called successive diagonalization, the second approach is based on analytical models that can be found for some special J's and the third method is based on an abstract theorem of Rozenbljum.