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arXiv 2302.04680cs.LGcs.AI
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具有质量保证的马氏链的混合学习

Learning Mixtures of Markov Chains with Quality Guarantees

Boston University(波士顿大学)

Fabian Spaeh, Charalampos E. Tsourakakis

摘要:

大量的现代应用程序,从在线听歌和浏览网页到使用智能手机上的导航应用程序,都会产生大量的用户轨迹。将这些踪迹聚集成具有共同序列模式的组可以揭示人类行为的重要结构,可以通过更好的推荐改善用户体验,甚至防止自杀[LMCR 14]。数学建模这个问题的一种方法是作为马尔可夫链的混合。最近,Gupta,Kumar和Vassilvitski [GKV 16]介绍了一种基于奇异值分解(SVD)的算法(GKV-SVD),该算法在某些条件下可以完美地恢复n个状态上的L个链的混合物,仅给出长度为3的踪迹(3-trail)的分布。在这项工作中,我们通过强调和解决GKV-SVD算法[GKV 16]的两个重要约束来解决非混合马尔可夫链的问题:混合物中的一些链甚至可能不是弱连接的,其次,在实践中,人们事先不知道链的真实数量。我们在Gupta等人的论文[GKV 16]中解决了这些问题。具体来说,我们提出了一个代数标准,使我们能够有效地选择L的值,避免过拟合。此外,我们设计了一个重建算法,输出真实的混合物中存在的断开链,是强大的噪声。我们补充我们的理论结果与实验的合成和真实的数据,我们观察到,我们的方法优于GKV-SVD算法。最后,我们根据经验观察到,EM算法与我们的方法相结合,在实践中表现最好,无论是在重建误差方面的3-trails的分布和马尔可夫链的混合物。

英文摘要:

A large number of modern applications ranging from listening songs online and browsing the Web to using a navigation app on a smartphone generate a plethora of user trails. Clustering such trails into groups with a common sequence pattern can reveal significant structure in human behavior that can lead to improving user experience through better recommendations, and even prevent suicides [LMCR14]. One approach to modeling this problem mathematically is as a mixture of Markov chains. Recently, Gupta, Kumar and Vassilvitski [GKV16] introduced an algorithm (GKV-SVD) based on the singular value decomposition (SVD) that under certain conditions can perfectly recover a mixture of L chains on n states, given only the distribution of trails of length 3 (3-trail). In this work we contribute to the problem of unmixing Markov chains by highlighting and addressing two important constraints of the GKV-SVD algorithm [GKV16]: some chains in the mixture may not even be weakly connected, and secondly in practice one does not know beforehand the true number of chains. We resolve these issues in the Gupta et al. paper [GKV16]. Specifically, we propose an algebraic criterion that enables us to choose a value of L efficiently that avoids overfitting. Furthermore, we design a reconstruction algorithm that outputs the true mixture in the presence of disconnected chains and is robust to noise. We complement our theoretical results with experiments on both synthetic and real data, where we observe that our method outperforms the GKV-SVD algorithm. Finally, we empirically observe that combining an EM-algorithm with our method performs best in practice, both in terms of reconstruction error with respect to the distribution of 3-trails and the mixture of Markov Chains.

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