Sentences are used as nodes in the graph and the computational process can be described as: where PR(s i ) is the score of sentence s i and |S| denotes the number of sentences in a document cluster.
nowadays, some machine learning algorithms have also been applied in summarization for learning optimal feature weights automatically, for instance, some leaning to rank models (Svore et al., 2007;Jin et al., 2010;Shen and Li, 2011) have been introduced in summarization tasks.