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1.
Given a set of points
and ε>0, we propose and analyze an algorithm for the problem of computing a (1+ε)-approximation to the minimum-volume axis-aligned ellipsoid enclosing
. We establish that our algorithm is polynomial for fixed ε. In addition, the algorithm returns a small core set
, whose size is independent of the number of points m, with the property that the minimum-volume axis-aligned ellipsoid enclosing
is a good approximation of the minimum-volume axis-aligned ellipsoid enclosing
. Our computational results indicate that the algorithm exhibits significantly better performance than the theoretical worst-case
complexity estimate.
This work was supported in part by the National Science Foundation through CAREER Grants CCF-0643593 and DMI-0237415. 相似文献
2.
In the study of the asymptotic behaviour of solutions of differential-difference equations the
-spectrum has been useful, where
and
implies Fourier transform
, with
given
, φ∈L
∞(ℝ,X), X a Banach space,
(half)line. Here we study
and related concepts, give relations between them, especially
weak Laplace half-line spectrum of φ, and thus ⊂ classical Beurling spectrum = Carleman spectrum =
; also
= Beurling spectrum of “φ modulo
” (Chill-Fasangova). If
satisfies a Loomis type condition (L
U
), then
countable and
uniformly continuous ∈U are shown to imply
; here (L
U
) usually means
, indefinite integral Pf of f in U imply Pf in
(the Bohl-Bohr theorem for
= almost periodic functions, U=bounded functions). This spectral characterization and other results are extended to unbounded functions via mean classes
, ℳ
m
U ((2.1) below) and even to distributions, generalizing various recent results for uniformly continuous bounded φ. Furthermore for solutions of convolution systems S*φ=b with
in some
we show
. With these above results, one gets generalizations of earlier results on the asymptotic behaviour of solutions of neutral
integro-differential-difference systems. Also many examples and special cases are discussed. 相似文献
3.
Emanuele Delucchi 《Journal of Algebraic Combinatorics》2007,26(4):477-494
Given a finite group G and a natural number n, we study the structure of the complex of nested sets of the associated Dowling lattice
(Proc. Internat. Sympos., 1971, pp. 101–115) and of its subposet of the G-symmetric partitions
which was recently introduced by Hultman (, 2006), together with the complex of G-symmetric phylogenetic trees
. Hultman shows that the complexes
and
are homotopy equivalent and Cohen–Macaulay, and determines the rank of their top homology.
An application of the theory of building sets and nested set complexes by Feichtner and Kozlov (Selecta Math. (N.S.)
10, 37–60, 2004) shows that in fact
is subdivided by the order complex of
. We introduce the complex of Dowling trees
and prove that it is subdivided by the order complex of
. Application of a theorem of Feichtner and Sturmfels (Port. Math. (N.S.)
62, 437–468, 2005) shows that, as a simplicial complex,
is in fact isomorphic to the Bergman complex of the associated Dowling geometry.
Topologically, we prove that
is obtained from
by successive coning over certain subcomplexes. It is well known that
is shellable, and of the same dimension as
. We explicitly and independently calculate how many homology spheres are added in passing from
to
. Comparison with work of Gottlieb and Wachs (Adv. Appl. Math.
24(4), 301–336, 2000) shows that
is intimely related to the representation theory of the top homology of
.
Research partially supported by the Swiss National Science Foundation, project PP002-106403/1. 相似文献
4.
In this paper, we study a class of vector minimization problems on a complete metric space X which is identified with the corresponding complete metric space of objective functions
. We do not impose any compactness assumption on X. We show that, for most (in the sense of Baire category) functions
, the corresponding vector optimization problem has a solution. 相似文献
5.
Let be a field and q be a nonzero element of that is not a root of unity. We give a criterion for 〈0〉 to be a primitive ideal of the algebra of quantum matrices. Next, we describe all height one primes of ; these two problems are actually interlinked since it turns out that 〈0〉 is a primitive ideal of whenever has only finitely many height one primes. Finally, we compute the automorphism group of in the case where m ≠ n. In order to do this, we first study the action of this group on the prime spectrum of . Then, by using the preferred basis of and PBW bases, we prove that the automorphism group of is isomorphic to the torus when m ≠ n and (m,n) ≠ (1, 3),(3, 1).
This research was supported by a Marie Curie Intra-European Fellowship within the 6th European Community Framework Programme
and by Leverhulme Research Interchange Grant F/00158/X. 相似文献
6.
J. Bagherian Ilia Ponomarenko A. Rahnamai Barghi 《Journal of Algebraic Combinatorics》2008,27(2):173-185
We introduce a concept of cyclotomic association scheme over a finite near-field
. It is proved that any isomorphism of two such nontrivial schemes is induced by a suitable element of the group AGL(V), where V is the linear space associated with
. A sufficient condition on a cyclotomic scheme
that guarantee the inclusion
where
is a finite field with
elements, is given.
I. Ponomarenko partially supported by RFFI, grants 03-01-00349, NSH-2251.2003.1. 相似文献
7.
Given an open set in , we prove that every function in is zero everywhere on the boundary if and only if is regular in capacity. If in addition is bounded, then it is regular in capacity if and only if the mapping from into is injective, where denotes the Perron solution of the Dirichlet problem. Let be the set of all open subsets of which are regular in capacity. Then one can define metrics and on only involving the resolvent of the Dirichlet Laplacian. Convergence in those metrics will be defined to be the local/global uniform convergence of the resolvent of the Dirichlet Laplacian applied to the constant function . We prove that the spaces and are complete and contain the set of all open sets which are regular in the sense of Wiener (or Dirichlet regular) as a closed subset. 相似文献
8.
The aim of this paper is to give some representation formulas of Riesz and Poisson-Jensen type for super-solutions to a class
of hypoelliptic ultraparabolic operators on a homogeneous Lie group . Our results complete the ones obtained in Cinti (Math Scand 100:1–21, 2007). We also provide a suitable theory for -Green functions and for -Green potentials of Radon measures. The proofs mostly rely on the use of appropriate techniques relevant to the Potential
Theory for .
Investigation supported by University of Bologna. Funds for selected research topics. 相似文献
9.
Martin Kassabov 《Inventiones Mathematicae》2007,170(2):327-354
We construct explicit generating sets S
n
and of the alternating and the symmetric groups, which turn the Cayley graphs and into a family of bounded degree expanders for all n. 相似文献
10.
Let be the kernel of the natural map Out(Fn)→GLn(ℤ). We use combinatorial Morse theory to prove that has an Eilenberg–MacLane space which is (2n-4)-dimensional and that is not finitely generated (n≥3). In particular, this shows that the cohomological dimension of is equal to 2n-4 and recovers the result of Krstić–McCool that is not finitely presented. We also give a new proof of the fact, due to Magnus, that is finitely generated. 相似文献
11.
Hendrik Hubrechts 《Foundations of Computational Mathematics》2008,8(1):137-169
Let E
Γ be a family of hyperelliptic curves defined by
, where
is defined over a small finite field of odd characteristic. Then with
in an extension degree n field over this small field, we present a deterministic algorithm for computing the zeta function of the curve
by using Dwork deformation in rigid cohomology. The time complexity of the algorithm is
and it needs
bits of memory. A slight adaptation requires only
space, but costs time
. An implementation of this last result turns out to be quite efficient for n big enough.
H. Hubrechts is a Research Assistant of the Research Foundation–Flanders (FWO–Vlaanderen). 相似文献
12.
Z. -Q. Chen P. J. Fitzsimmons K. Kuwae T. -S. Zhang 《Probability Theory and Related Fields》2008,140(1-2):239-275
We present a path-space integral representation of the semigroup associated with the quadratic form obtained by a lower-order perturbation of the L 2-infinitesimal generator $\mathcal {L}We present a path-space integral representation of the semigroup associated with the quadratic form obtained by a lower-order
perturbation of the L
2-infinitesimal generator of a general symmetric Markov process. An illuminating concrete example for is , where D is a bounded Euclidean domain in is the Laplace operator in D with zero Dirichlet boundary condition and is the fractional Laplacian in D with zero exterior condition. The strong Markov process corresponding to is a Lévy process that is the sum of Brownian motion in and an independent symmetric (2s)-stable process in killed upon exiting the domain D. This probabilistic representation is a combination of Feynman-Kac and Girsanov formulas. Crucial to the development is the
use of an extension of Nakao’s stochastic integral for zero-energy additive functionals and the associated It? formula, both
of which were recently developed in Chen et al. [Stochastic calculus for Dirichlet processes (preprint)(2006)].
The research of T.-S. Zhang is supported by the British EPSRC. 相似文献
13.
A. J. Zaslavski 《Journal of Optimization Theory and Applications》2009,141(1):217-230
We study a class of vector minimization problems on a complete metric space X which is identified with the corresponding complete metric space of lower semicontinuous bounded-from-below objective functions
. We establish the existence of a G
δ
everywhere dense subset ℱ of
such that, for any objective function belonging to ℱ, the corresponding minimization problem possesses a solution. 相似文献
14.
Let B be a nilpotent matrix and suppose that its Jordan canonical form is determined by a partition λ. Then it is known that its
nilpotent commutator is an irreducible variety and that there is a unique partition μ such that the intersection of the orbit of nilpotent matrices corresponding to μ with is dense in . We prove that map given by is an idempotent map. This answers a question of Basili and Iarrobino [9] and gives a partial answer to a question of Panyushev [18]. In the proof, we use the fact that for a generic matrix the algebra generated by A and B is a Gorenstein algebra. Thus, a generic pair of commuting nilpotent matrices generates a Gorenstein algebra. We also describe
in terms of λ if has at most two parts. 相似文献
15.
16.
Tomoyuki Arakawa 《Inventiones Mathematicae》2007,169(2):219-320
We study the representation theory of the -algebra associated with a simple Lie algebra at level k. We show that the “-” reduction functor is exact and sends an irreducible module to zero or an irreducible module at any
level k∈ℂ. Moreover, we show that the character of each irreducible highest weight representation of is completely determined by that of the corresponding irreducible highest weight representation of affine Lie algebra of . As a consequence we complete (for the “-” reduction) the proof of the conjecture of E. Frenkel, V. Kac and M. Wakimoto on
the existence and the construction of the modular invariant representations of -algebras.
Mathematics Subject Classification (1991) 17B68, 81R10 相似文献
17.
18.
Vladimir Markovic 《Inventiones Mathematicae》2007,168(3):523-566
In this paper, we show that the mapping class group of a closed surface can not be geometrically realized as a group of homeomorphisms
of that surface. More precisely, let denote the standard projection of the group of homeomorphisms to the mapping class group of a closed surface M of genus g>5. We show that there is no homomorphism , such that is the identity. This answers a question by Thurston (see [11]).
Mathematics Subject Classification (2000) Primary 20H10, 37F30 相似文献
19.
Inspired by the work of Paterson on C
*
-algebras of directed graphs, we show how to associate a groupoid
to an ultragraph
in such a way that the C
*-algebra of
is canonically isomorphic to Tomforde’s C
*-algebra
. The groupoid
is built from an inverse semigroup
naturally associated to
.
A.E. Marrero was supported by grants from the National Science Foundation and the Sloan Foundation and by a GAANN Fellowship.
Many of the results here are taken from this author’s dissertation [7].
P.S. Muhly was supported by a grant from the National Science Foundation (DMS-0355443). 相似文献
20.
B. T. Kien N. C. Wong J. C. Yao 《Journal of Optimization Theory and Applications》2007,135(3):515-530
We study the following generalized quasivariational inequality problem: given a closed convex set X in a normed space E with the dual E
*, a multifunction
and a multifunction Γ:X→2
X
, find a point
such that
,
. We prove some existence theorems in which Φ may be discontinuous, X may be unbounded, and Γ is not assumed to be Hausdorff lower semicontinuous.
The authors express their sincere gratitude to the referees for helpful suggestions and comments.
This research was partially supported by a grant from the National Science Council of Taiwan, ROC.
B.T. Kien was on leave from National University of Civil Engineering, Hanoi, Vietnam. 相似文献