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91.
Ivana Bochicchio Ettore Laserra Agata Longobardi Enrico Mazziotti 《Ricerche di matematica》2012,61(2):219-230
This work is focused on the geometrical and physical characteristics of the class of reference frames associated to harmonic coordinates. Precisely, we express in relative form the harmonicity conditions and consider the so called ??spatially harmonicity?? of a reference frame in spherical symmetry. The initial data problem is then analyzed in polar coordinates and the obtained results are applied to special cases of exact solutions. 相似文献
92.
93.
Nicola Arcozzi Enrico Casadio Tarabusi Fausto Di Biase Massimo A. Picardello 《Transactions of the American Mathematical Society》2006,358(6):2781-2798
We establish a potential theoretic approach to the study of twist points in the boundary of simply connected planar domains.
94.
We present a constructive proof in Bishop’s style of Lebesgue’s dominated convergence theorem in the abstract setting of ordered uniform spaces. The proof generalises to this setting a classical proof in the framework of uniform lattices presented by Hans Weber in [Uniform lattices. II: order continuity and exhaustivity, Annali di Matematica pura ed applicata, (IV) CLXV (1993) 133-158]. 相似文献
95.
96.
An alleged weakness of heuristic optimisation methods is the stochastic character of their solutions: instead of finding the
truly optimal solution, they only provide a stochastic approximation of this optimum. In this paper we look into a particular
application, portfolio optimisation. We demonstrate that the randomness of the ‘optimal’ solution obtained from the algorithm
can be made so small that for all practical purposes it can be neglected. More importantly, we look at the relevance of the
remaining uncertainty in the out-of-sample period. The relationship between in-sample fit and out-of-sample performance is
not monotonous, but still, we observe that up to a point better solutions in-sample lead to better solutions out-of-sample.
Beyond this point there is no more cause for improving the solution any further: any in-sample improvement leads out-of-sample
only to financially meaningless improvements and unpredictable changes (noise) in performance. 相似文献
97.
Loss aversion with multiple investment goals 总被引:1,自引:0,他引:1
Enrico G. De Giorgi 《Mathematics and Financial Economics》2011,5(3):203-227
This paper presents a time-continuous portfolio selection model with loss averse investors, who possess multiple investment goals at different time horizons. The model assumes partial narrow framing. Investors follow a two-step approach. First, they optimally allocate wealth among investment goals. Second, they determine an optimal investment strategy for each investment goal separately. We show that when loss aversion is according to the experimental findings, investors mainly invest their wealth to reach long-term goals and adopt investment strategies with high leverage to reach short-term goals. The overall strategy also display high leverage. The same patterns is observed when loss aversion is extreme and goals are very ambitious. By contrast, when loss aversion is extreme but goals are not too ambitious, investors mainly invest to reach short-term goals and adopt safe investment strategies for this purpose. 相似文献
98.
Ewa M. Bednarczuk Enrico Miglierina Elena Molho 《Set-Valued and Variational Analysis》2011,19(4):569-587
The mountain pass theorem for scalar functionals is a fundamental result of the minimax methods in variational analysis. In this work we extend this theorem to the class of \(\mathcal{C}^{1}\) functions \(f:\mathbb{R}^{n}\rightarrow\mathbb{R}^{m}\), where the image space is ordered by the nonnegative orthant \(\mathbb{R}_{+}^{m}\). Under suitable geometrical assumptions, we prove the existence of a critical point of f and we localize this point as a solution of a minimax problem. We remark that the considered minimax problem consists of an inner vector maximization problem and of an outer set-valued minimization problem. To deal with the outer set-valued problem we use an ordering relation among subsets of \(\mathbb{R}^{m}\) introduced by Kuroiwa. In order to prove our result, we develop an Ekeland-type principle for set-valued maps and we extensively use the notion of vector pseudogradient. 相似文献
99.
100.
Rafael Ortega Enrico Serra Massimo Tarallo 《Proceedings of the American Mathematical Society》2000,128(9):2659-2665
A well known theorem says that the forced pendulum equation has periodic solutions if there is no friction and the external force has mean value zero. In this paper we show that this result cannot be extended to the case of linear friction.