Computes and stores the similarity matrix

def fit(self, weighted, show_progress=True):
        """ Computes and stores the similarity matrix """
        self.similarity = all_pairs_knn(weighted, self.K,
                                        show_progress=show_progress,
                                        num_threads=self.num_threads).tocsr()
        self.scorer = NearestNeighboursScorer(self.similarity)