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111.
Nikolaos S. Papageorgiou 《Rendiconti del Circolo Matematico di Palermo》1993,42(3):338-346
In this paper we consider a discrete-time, infinite horizon growth model for a multisector economy with an infinite dimensional commodity space, and we establish the existence of a weakly maximal optimal stationary program. 相似文献
112.
A key challenge for call centres remains the forecasting of high frequency call arrivals collected in hourly or shorter time buckets. In addition to the complex intraday, intraweek and intrayear seasonal cycles, call arrival data typically contain a large number of anomalous days, driven by the occurrence of holidays, special events, promotional activities and system failures. This study evaluates the use of a variety of univariate time series forecasting methods for forecasting intraday call arrivals in the presence of such outliers. Apart from established, statistical methods, we consider artificial neural networks (ANNs). Based on the modelling flexibility of the latter, we introduce and evaluate different methods to encode the outlying periods. Using intraday arrival series from a call centre operated by one of Europe’s leading entertainment companies, we provide new insights on the impact of outliers on the performance of established forecasting methods. Results show that ANNs forecast call centre data accurately, and are capable of modelling complex outliers using relatively simple outlier modelling approaches. We argue that the relative complexity of ANNs over standard statistical models is offset by the simplicity of coding multiple and unknown effects during outlying periods. 相似文献
113.
Kai Zhou Mustafa R. Kılınç Xi Chen Nikolaos V. Sahinidis 《Journal of Global Optimization》2018,70(3):497-516
Solving mixed-integer nonlinear programming (MINLP) problems to optimality is a NP-hard problem, for which many deterministic global optimization algorithms and solvers have been recently developed. MINLPs can be relaxed in various ways, including via mixed-integer linear programming (MIP), nonlinear programming, and linear programming. There is a tradeoff between the quality of the bounds and CPU time requirements of these relaxations. Unfortunately, these tradeoffs are problem-dependent and cannot be predicted beforehand. This paper proposes a new dynamic strategy for activating and deactivating MIP relaxations in various stages of a branch-and-bound algorithm. The primary contribution of the proposed strategy is that it does not use meta-parameters, thus avoiding parameter tuning. Additionally, this paper proposes a strategy that capitalizes on the availability of parallel MIP solver technology to exploit multicore computing hardware while solving MINLPs. Computational tests for various benchmark libraries reveal that our MIP activation strategy works efficiently in single-core and multicore environments. 相似文献
114.
Dumitru Motreanu Viorica V. Motreanu Nikolaos S. Papageorgiou 《Monatshefte für Mathematik》2010,33(2):59-80
First we prove the existence of a nontrivial smooth solution for a p-Laplacian equation with a (p − 1)-linear nonlinearity and a noncoercive Euler functional, under hypotheses including resonant problems with respect to
the principal eigenvalue of (-Dp, W1,p0(Z)){(-{\it \Delta}_p,\,W^{1,p}_0(Z))} . Then, for the semilinear problem (i.e., p = 2), assuming nonuniform nonresonance at infinity and zero, we prove a multiplicity theorem which provides the existence
of at least three nontrivial solutions, two being of opposite constant sign. Our approach combines minimax techniques with
Morse theory and truncation arguments. 相似文献
115.
116.
Themistoklis Glavelis Nikolaos Ploskas Nikolaos Samaras 《Journal of computational science》2010,1(3):150-158
The purpose of this paper is to present a computational comparison of some well-known free mathematical programs. Specifically, these programs are FreeMat, Mathnium, Octave, R and Scilab. All these programs are designed in order to be used either in the scientific community or the industry. Moreover, an additional aim of this paper is to propose open source alternative software which can replace commercial mathematical software. Several issues concerning available operating system platforms, data structures, languages’ structure, matrix operations, program modularization, libraries, packages, profiling tools and online help facilities are addressed in this paper. Discussions on their weaknesses and strengths characteristics are presented. Finally, a speed comparison of some frequently used algorithms, procedures and operations within software is also presented. 相似文献
117.
In this paper, we consider a semilinear Neumann problem with an indefinite linear part and a Carathéodory nonlinearity which is superlinear near infinity and near zero, but does not satisfy the Ambrosetti-Rabinowitz condition. Using an abstract existence theorem for C1-functions having a local linking at the origin, we establish the existence of at least one nontrivial smooth solution. 相似文献
118.
Nikolaos L.Tsitsas 《计算数学(英文版)》2010,(6):864-878
Block matrices associated with discrete Trigonometric transforms (DTT's) arise in the mathematical modelling of several applications of wave propagation theory including discretizations of scatterers and radiators with the Method of Moments, the Boundary Element Method, and the Method of Auxiliary Sources. The DTT's are represented by the Fourier, Hartley, Cosine, and Sine matrices, which are unitary and offer simultaneous diagonalizations of specific matrix algebras. The main tool for the investigation of the aforementioned wave applications is the efficient inversion of such types of block matrices. To this direction, in this paper we develop an efficient algorithm for the inversion of matrices with U-diagonalizable blocks (U a fixed unitary matrix) by utilizing the U- diagonalization of each block and subsequently a similarity transformation procedure. We determine the developed method's computational complexity and point out its high efficiency compared to standard inversion techniques. An implementation of the algorithm in Matlab is given. Several numerical results are presented demonstrating the CPU-time efficiency and accuracy for ill-conditioned matrices of the method. The investigated matrices stem from real-world wave propagation applications. 相似文献
119.
Thomas Chen Nataša Pavlović Nikolaos Tzirakis 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2010
We consider solutions of the focusing cubic and quintic Gross–Pitaevskii (GP) hierarchies. We identify an observable corresponding to the average energy per particle, and we prove that it is a conserved quantity. We prove that all solutions to the focusing GP hierarchy at the L2-critical or L2-supercritical level blow up in finite time if the energy per particle in the initial condition is negative. Our results do not assume any factorization of the initial data. 相似文献
120.