困惑度、BLEU、ROUGE详解：语言模型评估指标计算与解读
从熵到困惑度，从 n-gram 到嵌入相似度，掌握评估指标的本质。本节基于《AI工程》第3章「Evaluation Methodology」— Understanding Language Modeling Metrics（熵、交叉熵、困惑度）、Exact Evaluation（BLEU、ROUGE、嵌入相似度）。
一、指标全景图
Chip Huyen 在《AI工程》第3章系统阐述了语言模型评估指标。理解这些指标是设计评估体系、解读模型表现的基础。书中将指标分为：语言建模指标（熵、困惑度）、精确评估（功能正确性、参考相似度、嵌入）。
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