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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
In this note we investigate the asymptotic behavior of the solutions of the heat equation with random, fast oscillating potential
${rcl} \partial_tu_{\varepsilon}(t,x)&=&\dfrac12\Delta_xu_{\varepsilon}(t,x)+{\varepsilon}^{-\gamma}V\left(\dfrac{x}{{\varepsilon}}\right)u_{\varepsilon}(t,x),\,(t,x)\in(0,+\infty)\times{\mathbb R}^d, \\ u_{\varepsilon}(0,x)&=&u_0(x),\,x\in{\mathbb R}^d, $\begin{array}{rcl} \partial_tu_{\varepsilon}(t,x)&=&\dfrac12\Delta_xu_{\varepsilon}(t,x)+{\varepsilon}^{-\gamma}V\left(\dfrac{x}{{\varepsilon}}\right)u_{\varepsilon}(t,x),\,(t,x)\in(0,+\infty)\times{\mathbb R}^d, \\ u_{\varepsilon}(0,x)&=&u_0(x),\,x\in{\mathbb R}^d, \end{array} 相似文献
962.
James M. Calvin 《Journal of Global Optimization》2010,48(1):17-27
This paper considers complexity bounds for the problem of approximating the global minimum of a univariate function when the
function evaluations are corrupted by random noise. We take an average-case point of view, where the objective function is
taken to be a sample function of a Wiener process and the noise is independent Gaussian. Previous papers have bounded the
convergence rates of some nonadaptive algorithms. We establish a lower bound on the convergence rate of any nonadaptive algorithm. 相似文献
963.
Francisco Cribari-Neto Maria da Glória A. Lima 《Annals of the Institute of Statistical Mathematics》2010,62(6):1053-1082
The linear regression model is commonly used by practitioners to model the relationship between the variable of interest and
a set of explanatory variables. The assumption that all error variances are the same, known as homoskedasticity, is oftentimes
violated when cross sectional data are used. Consistent standard errors for the ordinary least squares estimators of the regression
parameters can be computed following the approach proposed by White (Econometrica 48:817–838, 1980). Such standard errors,
however, are considerably biased in samples of typical sizes. An improved covariance matrix estimator was proposed by Qian
and Wang (J Stat Comput Simul 70:161–174, 2001). In this paper, we improve upon the Qian–Wang estimator by defining a sequence
of bias-adjusted estimators with increasing accuracy. The numerical results show that the Qian–Wang estimator is typically
much less biased than the estimator proposed by Halbert White and that our correction to the former can be quite effective
in small samples. Finally, we show that the Qian–Wang estimator can be generalized into a broad class of heteroskedasticity-consistent
covariance matrix estimators, and our results can be easily extended to such a class of estimators. 相似文献
964.
We consider the combined hubbing and routing problem in postal delivery systems and develop an iterative two-stage solution
procedure for the problem. In the first stage, hub locations are determined and postal offices are multiply allocated to the
hubs. The second stage gives the routes in hub regions that alter the distances between points used in the hub-location problem.
The procedure then iterates between two stages by updating the distances used in hubbing in order to produce a route-compatible
hub configuration. Computational experience is reported for the test problems taken from the literature. For a case study
Turkish postal delivery system data are utilized. As the case study is applied on a road network, a final stage, seeking improvements
based on special structures in the routed network, is appended to the two-stage solution procedure. 相似文献
965.
A multi-objective mixed integer programming model for equity portfolio construction and selection is developed in this study,
in order to generate the Pareto optimal portfolios, using a novel version of the well known ε-constraint method. Subsequently, an interactive filtering process is also proposed to assist the decision maker in making
his/her final choice among the Pareto solutions. The proposed methodology is tested through an application in the Athens Stock
Exchange. 相似文献
966.
Wiesława T. Obuchowska 《Journal of Global Optimization》2010,46(3):423-433
In this paper we investigate certain aspects of infeasibility in convex integer programs, where the constraint functions are
defined either as a composition of a convex increasing function with a convex integer valued function of n variables or the sum of similar functions. In particular we are concerned with the problem of an upper bound for the minimal
cardinality of the irreducible infeasible subset of constraints defining the model. We prove that for the considered class
of functions, every infeasible system of inequality constraints in the convex integer program contains an inconsistent subsystem
of cardinality not greater than 2
n
, this way generalizing the well known theorem of Scarf and Bell for linear systems. The latter result allows us to demonstrate
that if the considered convex integer problem is bounded below, then there exists a subset of at most 2
n
−1 constraints in the system, such that the minimum of the objective function subject to the inequalities in the reduced subsystem,
equals to the minimum of the objective function over the entire system of constraints. 相似文献
967.
We prove that a real function is operator monotone (operator convex) if the corresponding monotonicity (convexity) inequalities
are valid for some normal state on the algebra of all bounded operators in an infinite-dimensional Hilbert space. We describe
the class of convex operator functions with respect to a given von Neumann algebra in dependence of types of direct summands
in this algebra. We prove that if a function from ℝ+ into ℝ+ is monotone with respect to a von Neumann algebra, then it is also operator monotone in the sense of the natural order on
the set of positive self-adjoint operators affiliated with this algebra. 相似文献
968.
The purpose of this paper is to describe the structures of the Möbius semigroup induced by the Möbius transformation group (?, SL(2,?)). In particular, we study stabilizer subsemigoups of Möbius semigroup via the triangle semigroup. In this work, we obtained a geometric interpretation of the least contraction coefficient function of the Möbius semigroup via the triangle semigroup and investigated an extension of stabilizer subsemigoups of the Möbius semigroup. Finally, we obtained a factorization of our stabilizer subsemigoups of the Möbius semigroup. 相似文献
969.
Encoding the hierarchical structure of images by p-adic numbers allows for image processing and computer vision methods motivated from arithmetic physics. The p-adic Polyakov action leads to the p-adic diffusion equation in low level vision. Hierarchical segmentation provides another way of p-adic encoding. Then a topology on that finite set of p-adic numbers yields a hierarchy of topological models underlying the image. In the case of chain complexes, the chain maps
yield conditions for the existence of a hierarchy, and these can be expressed in terms of p-adic integrals. Such a chain complex hierarchy is a special case of a persistence complex from computational topology, where
it is used for computing persistence barcodes for shapes. The approach is motivated by the observation that using p-adic numbers often leads to more efficient algorithms than their real or complex counterparts. 相似文献
970.
Multivariate Hierarchical Copulas with Shocks 总被引:2,自引:0,他引:2
Fabrizio Durante Marius Hofert Matthias Scherer 《Methodology and Computing in Applied Probability》2010,12(4):681-694
A transformation to obtain new multivariate hierarchical copulas, starting with an arbitrary copula, is introduced. In addition
to the hierarchical structure, the presented construction principle explicitly supports singular components. These may be
interpreted as the effect of local or global shocks to the underlying random variables. A large spectrum of dependence patterns
can be achieved by the presented transformation, which seems promising for practical applications. Moreover, copulas arising
from this construction are similarly admissible with respect to analytical tractability and sampling routines as the original
copula. Finally, several well-known families of copulas may be interpreted as special cases. 相似文献
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