英文标题:
《Closedness of convex sets in Orlicz spaces with applications to dual
representation of risk measures》
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作者:
Niushan Gao, Denny H. Leung, Foivos Xanthos
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最新提交年份:
2017
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英文摘要:
Let $(\\Phi,\\Psi)$ be a conjugate pair of Orlicz functions. A set in the Orlicz space $L^\\Phi$ is said to be order closed if it is closed with respect to dominated convergence of sequences of functions. A well known problem arising from the theory of risk measures in financial mathematics asks whether order closedness of a convex set in $L^\\Phi$ characterizes closedness with respect to the topology $\\sigma(L^\\Phi,L^\\Psi)$. (See [26, p.3585].) In this paper, we show that for a norm bounded convex set in $L^\\Phi$, order closedness and $\\sigma(L^\\Phi,L^\\Psi)$-closedness are indeed equivalent. In general, however, coincidence of order closedness and $\\sigma(L^\\Phi,L^\\Psi)$-closedness of convex sets in $L^\\Phi$ is equivalent to the validity of the Krein-Smulian Theorem for the topology $\\sigma(L^\\Phi,L^\\Psi)$; that is, a convex set is $\\sigma(L^\\Phi,L^\\Psi)$-closed if and only if it is closed with respect to the bounded-$\\sigma(L^\\Phi,L^\\Psi)$ topology. As a result, we show that order closedness and $\\sigma(L^\\Phi,L^\\Psi)$-closedness of convex sets in $L^\\Phi$ are equivalent if and only if either $\\Phi$ or $\\Psi$ satisfies the $\\Delta_2$-condition. Using this, we prove the surprising result that: \\emph{If (and only if) $\\Phi$ and $\\Psi$ both fail the $\\Delta_2$-condition, then there exists a coherent risk measure on $L^\\Phi$ that has the Fatou property but fails the Fenchel-Moreau dual representation with respect to the dual pair $(L^\\Phi, L^\\Psi)$}. A similar analysis is carried out for the dual pair of Orlicz hearts $(H^\\Phi,H^\\Psi)$.
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中文摘要:
设$(\\Phi,\\Psi)$是Orlicz函数的共轭对。如果Orlicz空间$L^\\Phi$中的集合相对于函数序列的支配收敛是闭合的,则称其为顺序闭合的。金融数学中风险度量理论产生的一个众所周知的问题是,关于拓扑$\\ sigma(L ^ \\ Phi,L ^ \\ Psi)$,在$L ^ \\ Phi$中的凸集的序闭性是否表征了闭性。(见[26,第3585页])本文证明了对于$L^\\Phi$中的范数有界凸集,阶闭度和$\\sigma(L^\\Phi,L^\\Psi)$-闭度是等价的。然而,一般来说,$L^ \\ Phi$中凸集的阶闭性和$\\ sigma(L^ \\ Phi,L^ \\ Psi)$-闭性的重合等价于拓扑$\\ sigma(L^ \\ Phi,L^ \\ Psi)$的Krein-Smulian定理的有效性;也就是说,凸集是$\\sigma(L^\\Phi,L^\\Psi)$-闭合的当且仅当它是关于有界$\\sigma(L^\\Phi,L^\\Psi)$拓扑闭合的。结果表明,当且仅当$\\ Phi$或$\\ Psi$满足$\\ Delta\\u 2$条件时,$\\ Phi$中凸集的阶闭度和$\\ sigma(L ^ \\ Phi,L ^ \\ Psi)$-闭度是等价的。利用这一点,我们证明了一个令人惊讶的结果:\\ emph{如果(且仅当)$\\ Phi$和$\\ Psi$都不满足$\\ Delta\\u 2$-条件,那么在$L^ \\ Phi$上存在一个一致的风险度量,它具有Fatou属性,但不满足关于对偶$(L^ \\ Phi,L^ \\ Psi)$)的Fenchel-Moreau对偶表示。对双对Orlicz心脏$(H^\\Phi,H^\\Psi)$进行了类似的分析。
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分类信息:
一级分类:Quantitative Finance 数量金融学
二级分类:Mathematical Finance 数学金融学
分类描述:Mathematical and analytical methods of finance, including stochastic, probabilistic and functional analysis, algebraic, geometric and other methods
金融的数学和分析方法,包括随机、概率和泛函分析、代数、几何和其他方法
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