论文标题

通过Levenshtein变异自动编码器防止后塌陷

Preventing Posterior Collapse with Levenshtein Variational Autoencoder

论文作者

Havrylov, Serhii, Titov, Ivan

论文摘要

变分自动编码器(VAE)是诱导潜在变量模型的标准框架,这些模型在学习文本表示和文本生成方面已有效。使用VAE的关键挑战是{\ it后塌陷}问题:学习倾向于收敛到发电机忽略潜在变量的微不足道解决方案。在我们的Levenstein Vae中,我们建议用一个易于优化和防止后部崩溃的新目标代替下限(ELBO)的证据。直观地,它对应于从自动编码器中生成一个序列,并鼓励模型根据Levenshtein距离(LD)预测最佳延续,并在生成序列中的每个时间步骤中使用参考句子。我们从概率的角度来激励该方法,表明它与优化基于LD的核心核密度估计器与模型分布的棘手的kullback-leibler差异密切相关。有了这个目标,任何无视潜在变量的发电机都会遭受巨大的惩罚,因此不会发生后倒塌。我们将我们的方法与策略蒸馏\ Cite {Rossgb11}和Dynamic Oracles \ Cite {Goldbergn12}联系起来。通过考虑Yelp和SNLI基准测试,我们表明Levenstein Vae产生的潜在表示比预防后塌陷的替代方法更具信息性。

Variational autoencoders (VAEs) are a standard framework for inducing latent variable models that have been shown effective in learning text representations as well as in text generation. The key challenge with using VAEs is the {\it posterior collapse} problem: learning tends to converge to trivial solutions where the generators ignore latent variables. In our Levenstein VAE, we propose to replace the evidence lower bound (ELBO) with a new objective which is simple to optimize and prevents posterior collapse. Intuitively, it corresponds to generating a sequence from the autoencoder and encouraging the model to predict an optimal continuation according to the Levenshtein distance (LD) with the reference sentence at each time step in the generated sequence. We motivate the method from the probabilistic perspective by showing that it is closely related to optimizing a bound on the intractable Kullback-Leibler divergence of an LD-based kernel density estimator from the model distribution. With this objective, any generator disregarding latent variables will incur large penalties and hence posterior collapse does not happen. We relate our approach to policy distillation \cite{RossGB11} and dynamic oracles \cite{GoldbergN12}. By considering Yelp and SNLI benchmarks, we show that Levenstein VAE produces more informative latent representations than alternative approaches to preventing posterior collapse.

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