Some trivial considerations

1991 ◽  
Vol 56 (2) ◽  
pp. 624-631 ◽  
Author(s):  
John B. Goode
Keyword(s):  
Finite Rank ◽  
Stability Theory ◽  
Local Property ◽  
Geometrical Aspect ◽  
Categorical Theory ◽  
Superstable Theory ◽  
Local Character ◽  
Infinite Rank ◽  
Essential Properties ◽  
Rank One

At the source of what is now known as “geometric stability theory” was Zil'ber's intuition that the essential properties of an aleph-one-categorical theory were controlled by the geometries of its minimal types. (However, the situation is much more complex than was assumed in Zil'ber [1984], since the main conjecture of that paper has been disproved by Hrushovski.) This is not unnatural in this unidimensional case, where all these geometries have isomorphic contractions, but it was even realized later, in Cherlin, Harrington and Lachlan [1985] and Buechler [1986], that, for any superstable theory with finite ranks, a certain “local” property, i.e. a property satisfied by the geometry of each type of rank one (namely: to have a projective contraction), was equivalent to a “global” one (the theory is one-based, hence satisfies a coordinatization lemma). Then it was shown, in Pillay [1986], that this situation does not generalize to the infinite rank case, that, even for a theory of rank omega, the (local) assumption of projectivity for all the regular types of the theory does not have an exact global counterpart.To clarify this kind of phenomena, I suggest here the elimination of their geometrical aspect, considering only the case where all of the geometries are degenerate. I will study various notions of triviality, which make sense in a stable context, and turn out to be equivalent in the finite rank case; some of them have a definite global flavour, others are of local character.

scholarly journals Dimension of the Exceptional Set in the Aronszajn–Donoghue Theorem for Finite Rank Perturbations

2020 ◽  
Author(s):  
Constanze Liaw ◽  
Sergei Treil ◽  
Alexander Volberg
Keyword(s):  
Finite Rank ◽  
Measure Zero ◽  
Adjoint Operator ◽  
Cyclic Vector ◽  
Spectral Measures ◽  
Hermitian Matrices ◽  
Exceptional Set ◽  
Direct Sum ◽  
Rank One Perturbation ◽  
Rank One

Abstract The classical Aronszajn–Donoghue theorem states that for a rank-one perturbation of a self-adjoint operator (by a cyclic vector) the singular parts of the spectral measures of the original and perturbed operators are mutually singular. As simple direct sum type examples show, this result does not hold for finite rank perturbations. However, the set of exceptional perturbations is pretty small. Namely, for a family of rank $d$ perturbations $A_{\boldsymbol{\alpha }}:= A + {\textbf{B}} {\boldsymbol{\alpha }} {\textbf{B}}^*$, ${\textbf{B}}:{\mathbb C}^d\to{{\mathcal{H}}}$, with ${\operatorname{Ran}}{\textbf{B}}$ being cyclic for $A$, parametrized by $d\times d$ Hermitian matrices ${\boldsymbol{\alpha }}$, the singular parts of the spectral measures of $A$ and $A_{\boldsymbol{\alpha }}$ are mutually singular for all ${\boldsymbol{\alpha }}$ except for a small exceptional set $E$. It was shown earlier by the 1st two authors, see [4], that $E$ is a subset of measure zero of the space $\textbf{H}(d)$ of $d\times d$ Hermitian matrices. In this paper, we show that the set $E$ has small Hausdorff dimension, $\dim E \le \dim \textbf{H}(d)-1 = d^2-1$.

scholarly journals Mutual information for low-rank even-order symmetric tensor estimation

2020 ◽  
Author(s):  
Clément Luneau ◽  
Jean Barbier ◽  
Nicolas Macris
Keyword(s):  
Mutual Information ◽  
Finite Rank ◽  
Interpolation Method ◽  
Symmetric Tensor ◽  
Low Rank ◽  
Tensor Factorization ◽  
Adaptive Interpolation ◽  
Odd Order ◽  
Rank One ◽  
Even Order

Abstract We consider a statistical model for finite-rank symmetric tensor factorization and prove a single-letter variational expression for its asymptotic mutual information when the tensor is of even order. The proof applies the adaptive interpolation method originally invented for rank-one factorization. Here we show how to extend the adaptive interpolation to finite-rank and even-order tensors. This requires new non-trivial ideas with respect to the current analysis in the literature. We also underline where the proof falls short when dealing with odd-order tensors.

A Geometric Characterization of Nonnegative Bands

2004 ◽  
Vol 47 (2) ◽  
pp. 257-263
Author(s):  
Alka Marwaha
Keyword(s):  
Invariant Subspace ◽  
Geometric Structure ◽  
Finite Rank ◽  
Special Kind ◽  
Maximal Rank ◽  
Geometric Characterization ◽  
Idempotent Operators ◽  
Rank One ◽  
Standard Subspace

AbstractA band is a semigroup of idempotent operators. A nonnegative band S in having at least one element of finite rank and with rank (S) > 1 for all S in S is known to have a special kind of common invariant subspace which is termed a standard subspace (defined below).Such bands are called decomposable. Decomposability has helped to understand the structure of nonnegative bands with constant finite rank. In this paper, a geometric characterization of maximal, rank-one, indecomposable nonnegative bands is obtained which facilitates the understanding of their geometric structure.

On the number of nonisomorphic models of size |T|

1994 ◽  
Vol 59 (1) ◽  
pp. 41-59 ◽  
Author(s):  
Ambar Chowdhury
Keyword(s):  
Finite Rank ◽  
Superstable Theory

AbstractLet T be an uncountable, superstable theory. In this paper we proveTheorem A. If T has finite rank, then I(|T|, T) ≥ ℵ0.Theorem B. If T is trivial, then I(|T|, T) ≥ ℵ0.

SINGULARLY FINITE RANK NONSYMMETRIC PERTURBATIONS ${\mathcal H}_{-2}$-CLASS OF A SELF-ADJOINT OPERATOR

2021 ◽  
Vol 9 (1) ◽  
pp. 140-151
Author(s):  
O. Dyuzhenkova ◽  
M. Dudkin
Keyword(s):  
Finite Rank ◽  
Scalar Product ◽  
Separable Hilbert Space ◽  
Point Spectrum ◽  
Adjoint Operator ◽  
Formal Expression ◽  
Rank One Perturbation ◽  
Rank One ◽  
Negative Space ◽  
First Time

The singular nonsymmetric rank one perturbation of a self-adjoint operator from classes ${\mathcal H}_{-1}$ and ${\mathcal H}_{-2}$ was considered for the first time in works by Dudkin M.E. and Vdovenko T.I. \cite{k8,k9}. In the mentioned papers, some properties of the point spectrum are described, which occur during such perturbations. This paper proposes generalizations of the results presented in \cite{k8,k9} and \cite{k2} in the case of nonsymmetric class ${\mathcal H}_{-2}$ perturbations of finite rank. That is, the formal expression of the following is considered \begin{equation*} \tilde A=A+\sum \limits_{j=1}^{n}\alpha_j\langle\cdot,\omega_j\rangle\delta_j, \end{equation*} where $A$ is an unperturbed self-adjoint operator on a separable Hilbert space ${\mathcal H}$, $\alpha_j\in{\mathbb C}$, $\omega_j$, $\delta_j$, $j=1,2, ..., n<\infty$ are vectors from the negative space ${\mathcal H}_{-2}$ constructed by the operator $A$, $\langle\cdot,\cdot\rangle$ is the dual scalar product between positive and negative spaces.

scholarly journals Generating groups of certain soluble varieties

1974 ◽  
Vol 17 (2) ◽  
pp. 222-233 ◽  
Author(s):  
Narain Gupta ◽  
Frank Levin
Keyword(s):  
Free Group ◽  
Finite Rank ◽  
Free Groups ◽  
Infinite Rank ◽  
Variety Of Groups ◽  
Countably Infinite

Any variety of groups is generated by its free group of countably infinite rank. A problem that appears in various forms in Hanna Neumann's book [7] (see, for intance, sections 2.4, 2.5, 3.5, 3.6) is that of determining if a given variety B can be generated by Fk(B), one of its free groups of finite rank; and if so, if Fn(B) is residually a k-generator group for all n ≧ k. (Here, as in the sequel, all unexplained notation follows [7].)

COMMUTATOR SUBGROUPS OF FREE NILPOTENT GROUPS

2007 ◽  
Vol 17 (05n06) ◽  
pp. 1021-1031
Author(s):  
N. GUPTA ◽  
I. B. S. PASSI
Keyword(s):  
Nilpotent Group ◽  
Free Group ◽  
Finite Rank ◽  
Free Groups ◽  
Nilpotent Groups ◽  
Finite Chain ◽  
Free Nilpotent Group ◽  
Infinite Rank ◽  
Derived Subgroup ◽  
Finite Set

For fixed m, n ≥ 2, we examine the structure of the nth lower central subgroup γn(F) of the free group F of rank m with respect to a certain finite chain F = F(0) > F(1) > ⋯ > F(l-1) > F(l) = {1} of free groups in which F(k) is of finite rank m(k) and is contained in the kth derived subgroup δk(F) of F. The derived subgroups δk(F/γn(F)) of the free nilpotent group F/γn(F) are isomorphic to the quotients F(k)/(F(k) ∩ γn(F)) and admit presentations of the form 〈xk,1,…,xk,m(k): γ(n)(F(k))〉, where γ(n)(F(k)), contained in γn(F), is a certain partial lower central subgroup of F(k). We give a complete description of γn(F) as a staggered product Π1 ≤ k ≤ l-1(γ〈n〉(F(k))*γ[n](F(k)))F(k+1), where γ〈n〉(F(k)) is a free factor of the derived subgroup [F(k),F(k)] of F(k) having countable infinite rank and generated by a certain set of reduced commutators of weight at least n, and γ[n](F(k)) is the subgroup generated by a certain finite set of products of non-reduced ordered commutators of weight at least n. There are some far-reaching consequences.

scholarly journals On an Identity due to Bump and Diaconis, and Tracy and Widom

2011 ◽  
Vol 54 (2) ◽  
pp. 255-269 ◽  
Author(s):  
Paul-Olivier Dehaye
Keyword(s):  
Differential Operator ◽  
Random Matrix Theory ◽  
Random Matrix ◽  
Finite Rank ◽  
Symmetric Functions ◽  
Matrix Theory ◽  
Laguerre Polynomials ◽  
Symmetric Groups ◽  
Vertex Operators ◽  
Rank One

AbstractA classical question for a Toeplitz matrix with given symbol is how to compute asymptotics for the determinants of its reductions to finite rank. One can also consider how those asymptotics are affected when shifting an initial set of rows and columns (or, equivalently, asymptotics of their minors). Bump and Diaconis obtained a formula for such shifts involving Laguerre polynomials and sums over symmetric groups. They also showed how the Heine identity extends for such minors, which makes this question relevant to Random Matrix Theory. Independently, Tracy and Widom used the Wiener–Hopf factorization to express those shifts in terms of products of infinite matrices. We show directly why those two expressions are equal and uncover some structure in both formulas that was unknown to their authors. We introduce a mysterious differential operator on symmetric functions that is very similar to vertex operators. We show that the Bump–Diaconis–Tracy–Widom identity is a differentiated version of the classical Jacobi–Trudi identity.

The K-theory of the C*-algebra of foliations by slope components

2008 ◽  
Vol 3 (2) ◽  
pp. 221-260
Author(s):  
Catherine Oikonomides
Keyword(s):  
Large Class ◽  
Geometrical Aspect ◽  
C Algebra ◽  
Infinite Rank ◽  
Circle Bundles ◽  
K Theory

AbstractWe compute the K-theory of the C*-algebra for a large class of foliations of the 3-torus, which contains in particular all smooth foliated circle bundles over the 2-torus. This generalizes a well-known result of Torpe. We show that the rank of the K-theory groups reflect part of the geometrical aspect of the foliation. To illustrate these results, we compute some concrete examples, including a case where both K-theory groups have infinite rank.

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