We define the readability score as follows: where, given two adjacent sentences s i and s i+1 , w φ(s i , s i+1 ), which measures the connectivity of the two sentences, is the inner product of w and φ(s i , s i+1 ), w is a parameter vector and φ(s i , s i+1 ) is a feature vector of the two sentences.
the readability score of sentence sequence S is the sum of the connectivity of all adjacent sentences in the sequence.