在隐含依赖结构下,动态投资策略未必长期优于静态策略。
Sequential Portfolio Selection under Latent Side Information-Dependence Structure: Optimality and Universal Learning Algorithms
- 基于市场依赖结构与侧信息设计动态投资策略
- 动态策略增长速率最终趋近于静态策略,即使市场平稳
- 无需使用侧信息也能学习到接近最优的长期收益
本文研究在资产价格与部分不可观测的高维侧信息间存在隐含依赖结构的市场中,构建无卖空的最优序列投资策略问题。结果表明:即便拥有完整的依赖结构与市场信息,动态策略也未必能无限期地实现更高增长率。具体而言,若市场平稳(即依赖结构统计稳定),则利用全部市场信息的最优动态策略的增长率几乎必然随时间衰减至一个均衡状态,渐近收敛于常数策略的增长率。该工作重新审视了“仅当市场独立同分布时,常数策略才达到动态策略的最优极限增长率”的普遍认知。通过分析带侧信息的平稳市场中的动态对数最优策略,我们证明:即使动态策略不存在极限增长率,随机最优常数策略仍几乎必然存在。因此,本文讨论了两类投资组合学习算法,表明在学习过程中移除侧信息依然能保证渐近增长率接近最优动态策略。
原文摘要 · Abstract (English)
This paper investigates the investment problem of constructing an optimal no-short sequential portfolio strategy in a market with a latent dependence structure between asset prices and partly unobservable side information, which is often high-dimensional. The results demonstrate that a dynamic strategy, which forms a portfolio based on perfect knowledge of the dependence structure and full market information over time, may not grow at a higher rate infinitely often than a constant strategy, which remains invariant over time. Specifically, if the market is stationary, implying that the dependence structure is statistically stable, the growth rate of an optimal dynamic strategy, utilizing the maximum capacity of the entire market information, almost surely decays over time into an equilibrium state, asymptotically converging to the growth rate of a constant strategy. Technically, this work reassesses the common belief that a constant strategy only attains the optimal limiting growth rate of dynamic strategies when the market process is identically and independently distributed. By analyzing the dynamic log-optimal portfolio strategy as the optimal benchmark in a stationary market with side information, we show that a random optimal constant strategy almost surely exists, even when a limiting growth rate for the dynamic strategy does not. Consequently, two approaches to learning algorithms for portfolio construction are discussed, demonstrating the safety of removing side information from the learning process while still guaranteeing an asymptotic growth rate comparable to that of the optimal dynamic strategy.
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