共查询到20条相似文献,搜索用时 31 毫秒
1.
李师正 《纯粹数学与应用数学》1993,9(1):105-111
每个子半群是左理想的半群,称为左Hamilton半群,本文给出左Hamilton半群的刻划,并将左Hamilton半群表示为有向森林,最后给出左Hamilton半群同构的充要条件。 相似文献
2.
The purpose of this paper is to establish some new matching theorems in G-convex spaces and, as applications, to obtain some new fixed point theorems, section theorems and a minimax theorem in G-convex spaces. The results presented in this paper improve and generalize the corresponding results in [1], [2], [3], [4], [5], [7], [8], [9], [10], [11] and [12]. 相似文献
3.
1 IntroductionIt is well known that alternative theorenis and ntinimax tlleorenis fOr inequality systenismore or less liwo1ve sonle couvekity in their assun1Ptions(Refs. l-7). Generally convekity of afunctiou is related to certain couveXity of some set (Ref.&9). In this paper sonle new nAnmaxtl1eorems for bifunctions are obtailled. Tliese results are applied to derive saddle point tl1eorenis(Refs 10-13).In this paper we assume that X,Y Z and W are real locally collvex topological vectorsp… 相似文献
4.
Several existence theorems on multiple positive radial solutions of the elliptic boundary value problem in an exterior domain
are obtained by using the fixed point index theory. Our conclusions are essential improvements of the results in [7], [10]
and [13]. 相似文献
5.
We study the geometric properties of the base manifold for the unit tangent bundle satisfying the η-Einstein condition with
the canonical contact metric structure. One of the main theorems is that the unit tangent bundle of 4-dimensional Einstein
manifold, equipped with the canonical contact metric structure, is η-Einstein manifold if and only if the base manifold is
the space of constant sectional curvature 1 or 2.
Authors’ addresses: Y. D. Chai, S. H. Chun, J. H. Park, Department of Mathematics, Sungkyunkwan University, Suwon 440-746,
Korea; K. Sekigawa, Department of Mathematics, Faculty of Science, Niigata University, Niigata, 950-2181, Japan 相似文献
6.
Knut Petras 《Numerische Mathematik》2003,93(4):729-753
Summary. Some recent investigations (see e.g., Gerstner and Griebel [5], Novak and Ritter [9] and [10], Novak, Ritter and Steinbauer
[11], Wasilkowski and Woźniakowski [18] or Petras [13]) show that the so-called Smolyak algorithm applied to a cubature problem
on the d-dimensional cube seems to be particularly useful for smooth integrands. The problem is still that the numbers of nodes grow
(polynomially but) fast for increasing dimensions. We therefore investigate how to obtain Smolyak cubature formulae with a
given degree of polynomial exactness and the asymptotically minimal number of nodes for increasing dimension d and obtain their characterization for a subset of Smolyak formulae. Error bounds and numerical examples show their good behaviour
for smooth integrands. A modification can be applied successfully to problems of mathematical finance as indicated by a further
numerical example.
Received September 24, 2001 / Revised version received January 24, 2002 / Published online April 17, 2002
RID="*"
ID="*" The author is supported by a Heisenberg scholarship of the Deutsche Forschungsgemeinschaft 相似文献
7.
George Costakis 《Monatshefte für Mathematik》2005,145(1):11-17
In this work we deal with universal Taylor series in the open unit disk, in the sense of Nestoridis; see [12]. Such series are not (C,k) summable at every boundary point for every k; see [7], [11]. In the opposite direction, using approximation theorems of Arakeljan and Nersesjan we prove that universal Taylor series can be Abel summable at some points of the unit circle; these points can form any closed nowhere dense subset of the unit circle. 相似文献
8.
Stefano Serra 《Numerische Mathematik》1999,81(3):461-495
Summary. In previous works [21–23] we proposed the use of [5] and band Toeplitz based preconditioners for the solution of 1D and 2D boundary value problems (BVP) by means of the preconditioned
conjugate gradient (PCG) methods. As and band Toeplitz linear systems can be solved [4] by using fast sine transforms [8], these methods become especially attractive
in a parallel environment of computation. In this paper we extend this technique to the nonlinear, nonsymmetric case and,
in addition, we prove some clustering properties for the spectra of the preconditioned matrices showing why these methods
exhibit a convergence speed which results to be more than linear. Therefore these methods work much finer than those based on separable preconditioners [18,45], on incomplete LU factorizations
[36,13,27], and on circulant preconditioners [9,30,35] since the latter two techniques do not assure a linear rate of convergence.
On the other hand, the proposed technique has a wider range of application since it can be naturally used for nonlinear, nonsymmetric
problems and for BVP in which the coefficients of the differential operator are not strictly positive and only piecewise smooth.
Finally the several numerical experiments performed here and in [22,23] confirm the effectiveness of the theoretical analysis.
Received December 19, 1995 / Revised version received September 15, 1997 相似文献
9.
Mario Petrich 《Monatshefte für Mathematik》2000,129(4):329-340
A subsemigroup S of a semigroup Q is an order in Q if for every there exist such that , where a and d are contained in (maximal) subgroups of Q, and and are their inverses in these subgroups. A regular semigroup S is strict if it is a subdirect product of completely (0-)simple semigroups.
We construct all orders and involutions in Auinger’s model of a strict regular semigroup. This is used to find necessary and
sufficient conditions on an involution on an order S in a strict regular semigroup Q for extendibility to an involution on Q.
(Received 27 April 1999; in revised form 20 October 1999) 相似文献
10.
In answer to questions recently raised by Merel [Mer], we prove two non-vanishing theorems for the central value of automorphic
L-functions: let p be prime and let χ be a primitive character modulo p. Then for all p large enough
1. If χ is not quadratic and even, there exists a primitive weight 2 form f of level p with .
2. If χ is quadratic and even, then there exists a primitive weight 2 form f of level p with .
Received: 12 March 2000 / Revised version: 26 September 2000 相似文献
11.
Summary. In shape optimization problems, each computation of
the cost function by the finite element method
leads to an expensive analysis. The use of the second order derivative
can help to reduce the number of analyses. Fujii ([4], [10])
was the first to study this problem. J. Simon [19] gave the second order
derivative for the Navier-Stokes
problem, and the authors describe in [8], [11], a method which gives an
intrinsic expression of the first and second order derivatives on the
boundary
of the involved domain.
In this paper we study higher order derivatives. But one can ask
the following questions:
-- are they expensive to calculate?
-- are they complicated to use?
-- are they imprecise?
-- are they useless?
\medskip\noindent
At first sight, the answer seems to be positive, but classical results of
V. Strassen [20] and J. Morgenstern [13] tell us that the higher order
derivatives are not expensive to calculate, and can be computed
automatically. The purpose of this paper is to give an answer to the third
question by proving that the higher order derivatives of a function can be
computed with the same precision as the function itself.
We prove also that the derivatives so computed are
equal to the derivatives of the discrete problem (see Diagram 1). We
call the discrete
problem the finite dimensional problem processed by the computer. This result
allows the use of automatic differentiation ([5], [6]), which works only on
discrete problems.
Furthermore, the computations of Taylor's expansions
which are proposed at the end of this paper, could be a partial answer to
the last question.
Received January 27, 1993/Revised version received July 20, 1993 相似文献
12.
In [7], Nogueira and Rudolph proved that for irreducible permutations not of rotation class almost every (a.e.) interval
exchange transformation (i.e.t.) is topological weak mixing. It is conjectured that the claim holds if topological weak mixing
is replaced by weak mixing. Here we study the behaviour of eigenfunctions of i.e.t. Our analysis gives alternative proofs
of results due to Katok and Stepin [4] and Veech [10]: for certain permutations a.e. i.e.t. is weak mixing and for irreducible
permutations a.e. i.e.t. is totally ergodic.
(Received 1 February 2001) 相似文献
13.
Knut Smoczyk 《manuscripta mathematica》1998,95(2):225-236
Under the assumption of two a-priori bounds for the mean curvature, we are able to generalize a recent result due to Huisken
and Sinestrari [8], valid for mean convex surfaces, to a much larger class. In particular we will demonstrate that these a-priori
bounds are satisfied for a class of surfaces including meanconvex as well as starshaped surfaces and a variety of manifolds
that are close to them. This gives a classification of the possible singularities for these surfaces in the case n= 2. In addition we prove that under certain initial conditions some of them become mean convex before the first singularity
occurs.
Received: 6 June 1997 / Revised version: 24 October 1997 相似文献
14.
Yuk-Kam Lau 《Monatshefte für Mathematik》1999,128(2):111-129
Based on the method in Meurman [5], we study the mean square formula of the error term for a class of Arithmetical functions whose Dirichlet series satisfies
a functional equation with multiple gamma factors. We obtain improvements on some results of Chandrasekharan and Narasimhan [1].
(Received 29 June 1998; in final form 11 November 1998) 相似文献
15.
Juan José Torrens 《Numerische Mathematik》1997,76(1):69-85
Résumé. On établit des majorations de l'erreur d'approximation par éléments finis à partir de données de Lagrange pour des fonctions
appartenant à un espace de Sobolev d'ordre convenable, lorsque les degrés de liberté sont approchés à l'aide de la méthode
des plaquettes splines introduite par A. Le Méhauté (cf. [13], [14], [15]). Les résultats obtenus s'appliquent notamment
à la construction de surfaces de classe .
Received May 29, 1995 / Revised version received August 20, 1995 相似文献
16.
The upper limit and the first gap in the spectrum of genera of -maximal curves are known, see [34], [16], [35]. In this paper we determine the second gap. Both the first and second gaps
are approximately constant times , but this does not hold true for the third gap which is just 1 for while (at most) constant times q for This suggests that the problem of determining the third gap which is the object of current work on -maximal curves could be intricate. Here, we investigate a relevant related problem namely that of characterising those -maximal curves whose genus is equal to the third (or possible the forth) largest value in the spectrum. Our results also
provide some new evidence on -maximal curves in connection with Castelnuovo's genus bound, Halphen's theorem, and extremal curves.
Received: 1 January 2001 / Revised version: 30 July 2001 / Published online: 23 May 2002 相似文献
17.
Summary. We define the multivariate Padé-Bergman approximants (also called Padé approximants) and prove a natural generalization of de Montessus de Ballore theorem.
Numerous definitions of multivariate Padé approximants have already been introduced. Unfortunately, they all failed to generalize
de Montessus de Ballore theorem: either spurious singularities appeared (like the homogeneous Padé [3,4], or no general convergence
can be obtained due to the lack of consistency (like the equation lattice Padé type [3]).
Recently a new definition based on a least squares approach shows its ability to obtain the desired convergence [6]. We improve
this initial work in two directions. First, we propose to use Bergman spaces on polydiscs as a natural framework for stating
the least squares problem. This simplifies some proofs and leads us to the multivariate Padé approximants. Second, we pay a great attention to the zero-set of multivariate polynomials in order to find weaker (although
natural) hypothesis on the class of functions within the scope of our convergence theorem. For that, we use classical tools
from both algebraic geometry (Nullstellensatz) and complex analysis (analytic sets, germs).
Received December 4, 2001 / Revised version received January 2, 2002 / Published online April 17, 2002 相似文献
18.
Guoxin Wei 《Monatshefte für Mathematik》2006,149(4):343-350
By investigating hypersurfaces M
n
in the unit sphere S
n+1(1) with H
k
= 0 and with two distinct principal curvatures, we give a characterization of torus the
. We extend recent results of Perdomo [9], Wang [10] and Otsuki [8]. 相似文献
19.
Summary. In this paper, we derive the optimal error bounds for the stabilized MITC3 element [3], the MIN3 type element [7] and the T3BL element [8]. In this way we have
solved the problem proposed recently in [5] in a positive manner. Moreover, we estimate the difference between stabilized
MITC3 and MIN3 and show it is of order uniform in the plate thickness.
Received May 31, 2000 / Revised version received April 2, 2001 / Published online September 19, 2001 相似文献
20.
We extend two theorems due to P. Flavell [6] to arbitrary fusion systems.
Received: 18 June 2008 相似文献