Now showing items 21-40 of 378

• #### Interpolation in Bernstein and Paley-Wiener Spaces ﻿

[OWP-2008-04] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-08)
We construct closed sets S of arbitrarily small measure with the property: given any discrete set L, every l-function on L can be interpolated by an L-function with spectrum on F. This should be contrasted against ...
• #### Preconditioning of Block Tridiagonal Matrices ﻿

[OWP-2008-05] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-09)
Preconditioning methods via approximate block factorization for block tridiagonal matrices are studied. Bounds for the resulting condition numbers are given, and two methods for the recursive construction of the approximate ...
• #### Urn Models & Operator Ordering Procedures ﻿

[OWP-2008-06] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-10)
Ordering of operators is purely combinatorial task involving a number of commutators shuffling components of operator expression to desired form. Here we show how it can be illustrated by simple urn models in which normal ...
• #### Non-Standard Behavior of Density Estimators for Sums of Squared Observations ﻿

[OWP-2008-07] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-11)
It has been shown recently that, under an appropriate integrability condition, densities of functions of independent and identically distributed random variables can be estimated at the parametric rate by a local U-statistic, ...
• #### A Characterization of Semisimple Plane Polynomial Automorphisms ﻿

[OWP-2008-08] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-12)
It is well-known that an element of the linear group $GL_n(\mathbb{C})$ is semisimple if and only if its conjugacy class is Zariski closed. The aim of this paper is to show that the same result holds for the group of complex ...
• #### The Nagata automorphism is shifted linearizable ﻿

[OWP-2008-09] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-13)
A polynomial automorphism $F$ is called shifted linearizable if there exists a linear map $L$ such that $LF$ is linearizable. We prove that the Nagata automorphism $N:= (X-Y\Delta-Z\Delta^2,Y+Z\Delta,Z)$ where $\Delta=XZ+Y^2$ ...
• #### Nonlinear optimization over a Weighted Independence System ﻿

[OWP-2008-10] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-14)
We consider the problem of optimizing a nonlinear objective function over a weighted independence system presented by a linear-optimization oracle. We provide a polynomial-time algorithm that determines an r-best solution ...
• #### A 3-local characterization of Co2 ﻿

[OWP-2008-11] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-15)
Conway’s second largest simple group, $Co_2$, is characterized by the centralizer of an element of order 3 and certain fusion data.
• #### Noncommutative topological entropy of endomorphismus of Cuntz Algebras ﻿

[OWP-2008-12] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-16)
Noncommutative topological entropy estimates are obtained for ‘finite range’ endomorphisms of Cuntz algebras,generalising known results for the canonical shift endomorphisms. Exact values are computed for a class of ...
• #### Nonlinear Optimization for Matroid Intersection and Extensions ﻿

[OWP-2008-14] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-17)
We address optimization of nonlinear functions of the form $f(W_x)$ , where $f : \mathbb{R}^d \to \mathbb{R}$ is a nonlinear function, $W$ is a $d \times n$ matrix, and feasible $x$ are in some large finite set $\mathcal{F}$ ...
• #### Quantities that frequency-dependent selection maximizes ﻿

[OWP-2008-18] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-18)
We consider a model of frequency-dependent selection, to which we refer as the Wildcard Model, that accommodates as particular cases a number of diverse models of biologically specific situations. Two very different ...
• #### Epsilon-hypercyclic operators ﻿

[OWP-2008-19] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-19)
For each fixed number $\varepsilon$ in $(0, 1)$ we construct a bounded linear operator on the Banach space $\ell_1$ having a certain orbit which intersects every cone of aperture $\varepsilon$, but with every orbit avoiding ...
• #### Stratifying modular representations of finite groups ﻿

[OWP-2008-20] (Mathematisches Forschungsinstitut Oberwolfach, 2008-03-20)
We classify localising subcategories of the stable module category of a finite group that are closed under tensor product with simple (or, equivalently all) modules. One application is a proof of the telescope conjecture ...
• #### Proof mining in metric fixed point theory and ergodic theory ﻿

[OWP-2009-05] (Mathematisches Forschungsinstitut Oberwolfach, 2009)
In this survey we present some recent applications of proof mining to the fixed point theory of (asymptotically) nonexpansive mappings and to the metastability (in the sense of Terence Tao) of ergodic averages in uniformly ...
• #### Geometric quantization of integrable systems with hyperbolic singularities ﻿

[OWP-2009-01] (Mathematisches Forschungsinstitut Oberwolfach, 2009)
We construct the geometric quantization of a compact surface using a singular real polarization coming from an integrable system. Such a polarization always has singularities, which we assume to be of nondegenerate type. ...
• #### Minimal Riesz energy on the sphere for axis-supported external fields ﻿

[OWP-2009-04] (Mathematisches Forschungsinstitut Oberwolfach, 2009)
Abstract. We investigate the minimal Riesz $s$-energy problem for positive measures on the d-dimensional unit sphere $\mathbb{S}^d$ in the presence of an external field induced by a point charge, and more generally by ...
• #### Heisenberg-Weyl algebra revisited: combinatorics of words and paths ﻿

[OWP-2009-02] (Mathematisches Forschungsinstitut Oberwolfach, 2009)
The Heisenberg–Weyl algebra, which underlies virtually all physical representations of Quantum Theory, is considered from the combinatorial point of view. We provide a concrete model of the algebra in terms of paths on a ...
• #### Alternative iterative methods for nonexpansive mappings, rates of convergence and applications ﻿

[OWP-2009-19] (Mathematisches Forschungsinstitut Oberwolfach, 2009)
Alternative iterative methods for a nonexpansive mapping in a Banach space are proposed and proved to be convergent to a common solution to a fixed point problem and a variational inequality. We give rates of asymptotic ...
• #### On the non-analyticity locus of an arc-analytic function ﻿

[OWP-2009-03] (Mathematisches Forschungsinstitut Oberwolfach, 2009-02-21)
A function is called arc-analytic if it is real analytic on each real analytic arc. In real analytic geometry there are many examples of arc-analytic functions that are not real analytic. Arc analytic functions appear ...
• #### Pointwise hyperbolicity implies uniform hyperbolicity ﻿

[OWP-2009-06] (Mathematisches Forschungsinstitut Oberwolfach, 2009-02-23)
We provide a general mechanism for obtaining uniform information from pointwise data. A sample result is that if a diffeomorphism of a compact Riemannian manifold has pointwise expanding and contracting continuous invariant ...