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C. J. Maxson 《Results in Mathematics》2004,45(1-2):106-114
Let ε be the collection of those rings S such that, for every S-module V and every homogeneous function ?. V → V, ?(sv) = s?(v), s ∈ S, v ∈ V, ? is linear on V. In this paper we characterize those Stanley-Reisner rings, R, such that D(R) is in ε. 相似文献
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This paper presents an efficient active set method for computingthe lm solution of linear equations subject to linear constraints.The search direction of the proposed method is obtained viathe solution of a linear least-squares problem. It is shownthat the steepest-descent direction can be obtained by solvingthe same least-squares problem with simple bounds on the variables.This direction is used to prevent cycling at degenerate deadpoints. Numerical experiments illustrate the feasibility ofthe new method. 相似文献
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We consider the sets of moving-average and autoregressive processes and study their closures under the Mallows metric and the total variation convergence on finite dimensional distributions. These closures are unexpectedly large, containing nonergodic processes which are Poisson sums of i.i.d. copies from a stationary process. The presence of these nonergodic Poisson sum processes has immediate implications. In particular, identifiability of the hypothesis of linearity of a process is in question. A discussion of some of these issues for the set of moving-average processes has already been given without proof in Bickel and Bühlmann.(2) We establish here the precise mathematical arguments and present some additional extensions: results about the closure of autoregressive processes and natural sub-sets of moving-average and autoregressive processes which are closed.Research supported in part by grants NSA MDA 904-94-H-2020 and NSF DMS 95049555 相似文献
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Let R be commutative ring with identity and let M be an infinite unitary R-module. Call M homomorphically congruent (HC for short) provided M/N ? M for every submodule N of M for which |M/N| = |M|. In this article, we study HC modules over commutative rings. After a fairly comprehensive review of the literature, several natural examples are presented to motivate our study. We then prove some general results on HC modules, including HC module-theoretic characterizations of discrete valuation rings, almost Dedekind domains, and fields. We also provide a characterization of the HC modules over a Dedekind domain, extending Scott's classification over ? in [22]. Finally, we close with some open questions. 相似文献
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Cha Ji Hwan Finkelstein Maxim Levitin Gregory 《Methodology and Computing in Applied Probability》2022,24(3):1323-1340
Methodology and Computing in Applied Probability - A hybrid preventive maintenance policy for heterogeneous degrading items is discussed. It combines the classical age-replacement strategy, when a... 相似文献
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This paper produces several examples of varieties X for whichthe global sections functor (X,): DX-modD(X)-mod is exact,and makes D(X)-mod a quotient category of DX-mod, but is notan equivalence. These varieties are quotients by finite groupactions of D-affine varieties. The torsion of (X,) isalso described, in some cases. Here, Dx-mod denotes the categoryof quasi-coherent DX-modules. 相似文献
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Numerical analysis of a class of nonlinear duality problems is presented. One side of the duality is to minimize a sum of Euclidean norms subject to linear equality constraints (the constrained MSN problem). The other side is to maximize a linear objective function subject to homogeneous linear equality constraints and quadratic inequalities. Large sparse problems of this form result from the discretization of infinite dimensional duality problems in plastic collapse analysis.The solution method is based on the l
1 penalty function approach to the constrained MSN problem. This can be formulated as an unconstrained MSN problem for which the first author has recently published an efficient Newton barrier method, and for which new methods are still being developed.Numerical results are presented for plastic collapse problems with up to 180000 variables, 90000 terms in the sum of norms and 90000 linear constraints. The obtained accuracy is of order 10-8 measured in feasibility and duality gap. 相似文献
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Solutions of linear systems of equations are often known inadvance to belong to some closed convex set BRn. This informationleads to certain constraining strategies in iterative solutionalgorithms, such as the (nonlinear) projection of iterates ontoB. Convergence of resulting iterative processes and their limitsare studied. 相似文献
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Rasmussen Jakob G. Christensen Heidi S. 《Methodology and Computing in Applied Probability》2021,23(2):647-667
Methodology and Computing in Applied Probability - In this paper we consider point processes specified on directed linear networks, i.e. linear networks with associated directions. We adapt the... 相似文献
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O. D. Anderson 《The Journal of the Operational Research Society》1980,31(10):905-917
The paper describes a class of models rather more general than the ARIMA processes of Box and Jenkins, and surveys recently achieved results for their serial dependence behaviour. These properties are obtained analytically, from simulation and by direct computation-either approximately or exactly. The paper concentrates on the expectations of serial covariances and the problem of distinguishing between nearly non-stationary models and homogeneous non-stationary approximations to them-in particular, for a specific pair of ARMA(1,1) and IMA(1,1) processes. 相似文献
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Andreas Blass Frank Harary Zevi Miller 《Journal of Combinatorial Theory, Series B》1980,29(3):277-292
The link of a vertex v of a graph G is the subgraph induced by all vertices adjacent to v. If all the links of G are isomorphic to L, then G has constant link and L is called a link graph. We investigate the trees of order p≤9 to see which are link graphs. Group theoretic methods are used to obtain constructions of graphs G with constant link L for certain trees L. Necessary conditions are derived for the existence of a graph having a given graph L as its constant link. These conditions show that many trees are not link graphs. An example is given to show that a connected graph with constant link need not be point symmetric. 相似文献
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Teresa Bermúdez Antonio Martinón Emilio Negrín 《Integral Equations and Operator Theory》2010,68(3):301-312
We give a characterization of m-isometric operators on a separable Hilbert space. Moreover, we characterize the unilateral weighted shift operators which are m-isometries. 相似文献
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V. Chvtal 《Journal of Graph Theory》1990,14(5):555-558
We characterize (by forbidden induced subgraphs) those line-graphs that are perfectly orderable. Implicit in our presentation is a polynomial, time algorithm for recognizing these graphs. 相似文献
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Sotirios Bersimis Athanasios Sachlas Philippe Castagliola 《Methodology and Computing in Applied Probability》2017,19(4):1135-1149
In this paper, we introduce a methodology for efficiently monitoring a health process that classify the intervention outcome, in two dependent characteristics, as “absolutely successful”, “with minor but acceptable complications” and “unsuccessful due to severe complications”. The monitoring procedure is based on appropriate 2-dimensional scan rules. The run length distribution is acquired by studying the waiting time distribution for the first occurrence of a 2-dimensional scan in a bivariate sequence of trinomial trials. The waiting time distribution is derived through a Markov chain embedding technique. The proposed procedure is applied on two simulated cases while it is tested against a competing method showing an excellent performance. 相似文献