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  • 1
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_8954
    Format: 1 Online-Ressource (16 Seiten)
    Series Statement: Stochastic Programming E-Print Series 2003,2003,20
    Content: This paper considers the risk of employee pension accounts when there is a large weighting in company stock. The effect of reduced diversification and job related risk are considered. Mean-variance and scenario-based stochastic programming models are used for analysis. The stochastic porgramming formulation allows for fat tailed return distributions. Company stock is only optimal for employees with very low risk aversion or with very high return expectations for company stock. These conclusions are further strengthened when the possibility of job loss associated with poor company stock performance is included in the model. High observed weightings in company stock in DC pension plans are not explained by rational one-period models. Employees are bearing high levels of risk that is not rewarded, and that can lead to disastrous consequences.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 2
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9059
    Format: 1 Online-Ressource (17 Seiten)
    Content: When using the minimax approach one tries to hedge against the worst possible distribution belonging to a specified class P. A suitable stability analysis of results with respect to the choice of this class is an important issue. It has to be tailored to the type of the minimax problem, to the considered class of probability distributions and to the anticipated input perturbations. We shall focus on the effect of changes in input information for classes of probability distributions with support belonging to a given set and defined by (possibly perturbed) generalized moments values.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 3
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9053
    Format: 1 Online-Ressource (26 Seiten)
    Content: Formulation of stochastic optimisation problems and computational algorithms for their solution continue to make steady progress as can be seenfrom an analysis of many developments in this field. The edited volume by Wallace and Ziemba (2005) outlines both the SP modelling systems andmany applications in diverse domains.More recently, Fabozzi (2008) has considered the application of SP models to challenging financial engineering problems. The tightly knit yet highlyfocused group of researchers COSP: Committee on Stochastic Programming, their triennial international SP conference, and their active website points to the progressive acceptance of SP as a valuable decision tool. At the same time many of the major software vendors, namely, XPRESS, AIMMS, and MAXIMAL GAMS have started offering SP extensions to their optimisation suites.Our analysis of the modelling and algorithmic solver requirements reveals that (a) modelling support (b) scenario generation and (c) solutionmethods are three important aspects of a working SP system. Our research is focussed on all three aspects and we refer the readers to Valente et al.(2009) for modelling and Mitra et al. (2007) and Di Domenica et al. (2009) for scenario generation. In this paper we are concerned entirely with com-putational solution methods. Given the tremendous advance in LP solver algorithms there is certain amount of complacency that by constructing a”deterministic equivalent” problems it is possible to process most realistic instances of SP problems. In this paper we highlight the shortcoming of this line of argument. We describe the implementation and refinement of established algorithmic methods and report a computational study which clearly underpins the superior scale up properties of the solution methods which aredescribed in this paper.A taxonomy of the important class of SP problems may be found in Valente et al. (2008, 2009). The most important class of problems with manyapplications is the two-stage stochastic programming model with recourse, which originated from the early research of Dantzig (1955), Beale (1955) and Wets (1974).A comprehensive treatment of the model and solution methods can be found in Kall and Wallace (1994), Prekopa (1995), Birge and Louveaux (1997), Mayer (1998), Ruszczynski and Shapiro (2003), and Kall and Mayer (2005). Some of these monographs contain generalisations of the originalmodel. Colombo et al. (2006) and Gassmann and Wallace (1996) describe computational studies which are based on interior point method and simplex based methods respectively.The rest of this paper is organised in the following way. In section 2 we introduce the model setting of the two stage stochastic programming problem, in section 3 we consider a selection of solution methods for processing this class of problems. The established approaches of processing the deterministic equivalent LP form, the decomposition approach of Benders, the needfor regularisation are also discussed. We also introduce the concept of level decomposition and explain how it fits into the concept of regularisation. In section 4 we set out the computational study and in section 5 we summariseour conclusions.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 4
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9055
    Format: 1 Online-Ressource (27 Seiten)
    Content: Multi-period risk functionals assign a risk value to a discrete-time stochasticprocess $Y = (Y_1 , . . . , Y_T )$. While convexity and monotonicity properties extend ina natural way from the single-period case and several types of translation properties may be defined, the role of information becomes crucial in the multi-period situation. In this paper, we define multi-period functionals in a generic way, such that the available information (expressed as a filtration) enters explicitly the definition of the functional. This allows to study the information monotonicity property,which comes as the counterpart of value monotonicity. We discuss several ways ofconstructing concrete and computable functionals out of conditional risk mappingsand single-period risk functionals. Some of them appear as value functions of multistage stochastic programs, where the filtration appears in the non-anticipativity constraint. This approach leads in a natural way to information monotonicity. Thesubclass of polyhedral multi-period risk functionals becomes important for theiremployment in practical dynamic decision making and risk management. On the other hand, several functionals described in literature are not information-monotone, which limits their practical use.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 5
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9078
    Format: 1 Online-Ressource (31 Seiten)
    Content: We consider the solution of a system of stochastic generalized equations (SGE) where theunderlying functions are mathematical expectation of random set-valued mappings. SGE hasmany applications such as characterizing optimality conditions of a nonsmooth stochastic optimization problem and a stochastic equilibrium problem. We derive quantitative continuityof expected value of the set-valued mapping with respect to the variation of the underlyingprobability measure in a metric space. This leads to the subsequent qualitative and quantitative stability analysis of solution set mappings of the SGE. Under some metric regularityconditions, we derive Aubin’s property of the solution set mapping with respect to the changeof probability measure. The established results are applied to stability analysis of stationary points of classical one stage and two stage stochastic minimization problems, two stagestochastic mathematical programs with equilibrium constraints and stochastic programs withsecond order dominance constraints.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 6
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9106
    Format: 1 Online-Ressource (19 Seiten)
    Content: Scenarios are indispensable ingredients for the numerical solution of stochastic optimization problems. Earlier approaches for optimal scenario generation and reduction are based on stability arguments involving distances of probabilitymeasures. In this paper we review those ideas and suggest to make use of stability estimates based on distances containing minimal information, i.e., on data appearing in the optimization model only. For linear two-stage stochasticprograms we show that the optimal scenario generation problem can be reformulatedas best approximation problem for the expected recourse function and asgeneralized semi-infinite program, respectively. The latter model turns out to beconvex if either right-hand sides or costs are random. We also review the problemsof optimal scenario reduction for two-stage models and of optimal scenario generationfor chance constrained programs. Finally, we consider scenario generationand reduction for the classical newsvendor problem.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 7
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9066
    Format: 1 Online-Ressource (30 Seiten)
    Content: We define a risk averse nonanticipative feasible policy for multistage stochastic programsand propose a methodology to implement it. The approach is based on dynamic programmingequations written for a risk averse formulation of the problem.This formulation relies on a new class of multiperiod risk functionals called extended polyhedralrisk measures. Dual representations of such risk functionals are given and used to derive conditionsof coherence. In the one-period case, conditions for convexity and consistency with second orderstochastic dominance are also provided. The risk averse dynamic programming equations arespecialized considering convex combinations of one-period extended polyhedral risk measures suchas spectral risk measures.To implement the proposed policy, the approximation of the risk averse recourse functionsfor stochastic linear programs is discussed. In this context, we detail a stochastic dual dynamicprogramming algorithm which converges to the optimal value of the risk averse problem.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 8
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9065
    Format: 1 Online-Ressource (7 Seiten)
    Content: The paper deals with joint probabilistic constraints defined by a Gaussiancoefficient matrix. It is shown how to explicitly reduce the computation ofvalues and gradients of the underlying probability function to that of Gaussiandistribution functions. This allows to employ existing efficient algorithms forcalculating this latter class of function in order to solve probabilistically constrainedoptimization problems of the indicated type. Results are illustratedby an example from energy production.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 9
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9070
    Format: 1 Online-Ressource (17 Seiten)
    Content: We provide an explicit gradient formula for linear chance constraints under a (possibly singular) multivariate Gaussian distribution. This formula allows one to reduce the calculus of gradients to the calculus of values of the same type of chance constraints (in smaller dimension and with different distribution parameters). This is an important aspect for the numerical solution of stochastic optimization problems because existing efficient codes for e.g., calculating singular Gaussian distributions or regular Gaussian probabilities of polyhedra can be employed to calculate gradients at thesame time. Moreover, the precision of gradients can be controlled by that of function values, which is a great advantage over using finite difference approximations. Finally, higher order derivatives are easily derived explicitly. The use of the obtained formula is illustrated for an example of a stochastic transportation network.
    Language: English
    URL: Volltext  (kostenfrei)
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  • 10
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, Institut für Mathematik
    UID:
    edochu_18452_9096
    Format: 1 Online-Ressource (28 Seiten)
    Content: Quasi-Monte Carlo algorithms are studied for generating scenarios to solve two-stage linear stochastic programming problems. Their integrands are piecewise linear-quadratic, but do not belong to the function spaces consideredfor QMC error analysis. We show that under some weak geometric condition on the two-stage model all terms of their ANOVA decomposition, except the one of highest order, are continuously differentiable and second order mixed derivativesexist almost everywhere and belong to $L_2$. This implies that randomly shifted latticerules may achieve the optimal rate of convergence $O(n^{-1+\delta})$ with $\delta \in (0,\frac{1}{2}]$ and a constant not depending on the dimension if the effective superposition dimension is less than or equal to two. The geometric condition is shown to be satisfied for almost all covariance matrices if the underlying probability distribution isnormal. We discuss effective dimensions and techniques for dimension reduction.Numerical experiments for a production planning model with normal inputs showthat indeed convergence rates close to the optimal rate are achieved when usingrandomly shifted lattice rules or scrambled Sobol' point sets accompanied withprincipal component analysis for dimension reduction.
    Language: English
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