概率图模型之生成模型与判别模型

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July 30

概率图模型之生成模型与判别模型

     自然语言处理中，经常要处理序列标注问题（分词、词性标注、组快分析等），为给定的观察序列标注标记序列。

令o和s分别代表观察序列和标记序列，

根据贝叶斯公式，

1   生成模型和判别模型的定义

   对o和s进行统计建模，通常有两种方式：

(1)生成模型

   构建o和s的联合分布p(s,o)

(2)判别模型

   构建o和s的条件分布p(s|o)

2    判别模型和生成模型的对比

（1）训练时，二者优化准则不同

      生成模型优化训练数据的联合分布概率；

      判别模型优化训练数据的条件分布概率，判别模型与序列标记问题有较好的对应性。

（2）对于观察序列的处理不同

      生成模型中，观察序列作为模型的一部分；

      判别模型中，观察序列只作为条件，因此可以针对观察序列设计灵活的特征。

（3）训练复杂度不同

      判别模型训练复杂度较高。

（4）是否支持无指导训练

      生成模型支持无指导训练。

10:03 AM | Blog it

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