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Time-Consistent Portfolio Selection under Short-Selling Prohibition: From Discrete to Continuous Setting

Wong, Kwok Chuen orcid logoORCID: 0000-0001-7639-338X, Bensoussan, A., Yam, S. C. P. and Yung, S. P. (2014) Time-Consistent Portfolio Selection under Short-Selling Prohibition: From Discrete to Continuous Setting. SIAM Journal on Financial Mathematics, 5 . pp. 153-190. ISSN 1945-497X

Abstract
In this paper, we study the time consistent strategies in the mean-variance portfolio selection with short-selling prohibition in both discrete and continuous time settings. Recently, [T. Bjork, A. Murgoci, and X. Y. Zhou, Math. Finance, 24 (2014), pp. 1-24] considered the problem with state dependent risk aversion in the sense that the risk aversion is inversely proportional to the current wealth, and they showed that the time consistent control is linear in wealth. Considering the counterpart of their continuous time equilibrium control in the discrete time framework, the corresponding "optimal" wealth process can take negative values; and this negativity in wealth will lead the investor to a risk seeker which results in an unbounded value function that is economically unsound; even more, the limiting of the discrete solutions has shown to be their obtained continuous solution in [T. Bjork, A. Murgoci, and X. Y. Zhou, Math. Finance, 24 (2014), pp. 1-24]. To deal this limitation, we eliminate the chance of getting nonpositive wealth by prohibiting short-selling. Using backward induction, the equilibrium control in discrete time setting is shown to be linear in wealth. An application of the extended Hamilton-Jacobi-Bellman equation (see [T. Bjork and A. Murgoci, A General Theory of Markovian Time Inconsistent Stochastic Control Problems, working paper, Stockholm School of Economics, Stockholm, Sweden, 2010]) makes us also conclude that the continuous time equilibrium control is also linear in wealth with investment to wealth ratio satisfying an integral equation uniquely. We also show that the discrete time equilibrium controls converge to that in continuous time setting. Finally, in numerical studies, we illustrate that the constrained strategy in continuous setting can outperform the unconstrained one in some situations as depicted in Figure 8.
Metadata
Item Type:Article (Published)
Refereed:Yes
Uncontrolled Keywords:Humanities, Social Sciences
Subjects:Mathematics
Mathematics > Mathematical analysis
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health
DCU Faculties and Schools > Faculty of Science and Health > School of Mathematical Sciences
Publisher:Society for Industrial and Applied Mathematics
Official URL:https://epubs.siam.org/doi/10.1137/130914139
Copyright Information:Authors
ID Code:31245
Deposited On:16 Jul 2025 10:49 by Vidatum Academic . Last Modified 16 Jul 2025 10:49
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