说明：  用c#方法描述了话题识别（话题跟踪与检测）的过程，主要是提取特征词、特征词词频计算、权重计算（tfidf方法），进行相似度计算，最后聚类
(C# method describes the process of topic identification (topic tracking and detection), the word feature extraction, feature words word frequency calculation, weight to calculate methods (tfidf), similarity calculation, the final clustering)