用语言模型嵌入改进主题模型,不需微调即可提升效果。
Poisson-Process Topic Model for Integrating Knowledge from Pre-trained Language Models
- 将文档嵌入转为泊松点过程建模,每主题对应一个平滑强度函数。
- 在多个数据集上优于传统主题模型,理论收敛速率达最优当β≤1。
- 可无缝接入任意传统方法,且无需调整预训练模型参数。
传统主题模型基于词频,忽略上下文信息。本文利用预训练语言模型生成的上下文嵌入,将文档序列建模为泊松点过程,其强度度量为K个基测度(对应主题)的凸组合。提出一种灵活算法,结合净舍入与核平滑,融合传统主题模型方法。该框架将LLM视为黑箱,无需参数微调;同时支持任意传统方法作为模块接入。假设每个主题为嵌入空间上的β-霍尔德光滑强度测度,本文建立方法的收敛速率,并给出极小极大下界,证明当β≤1时收敛率可达最优。实验表明,该方法在多个数据集上显著优于传统方法。
原文摘要 · Abstract (English)
Topic modeling is traditionally applied to word counts without accounting for the context in which words appear. Recent advancements in large language models (LLMs) offer contextualized word embeddings, which capture deeper meaning and relationships between words. We aim to leverage such embeddings to improve topic modeling. We use a pre-trained LLM to convert each document into a sequence of word embeddings. This sequence is then modeled as a Poisson point process, with its intensity measure expressed as a convex combination of $K$ base measures, each corresponding to a topic. To estimate these topics, we propose a flexible algorithm that integrates traditional topic modeling methods, enhanced by net-rounding applied before and kernel smoothing applied after. One advantage of this framework is that it treats the LLM as a black box, requiring no fine-tuning of its parameters. Another advantage is its ability to seamlessly integrate any traditional topic modeling approach as a plug-in module, without the need for modifications Assuming each topic is a $β$-Hölder smooth intensity measure on the embedded space, we establish the rate of convergence of our method. We also provide a minimax lower bound and show that the rate of our method matches with the lower bound when $β\leq 1$. Additionally, we apply our method to several datasets, providing evidence that it offers an advantage over traditional topic modeling approaches.
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