npf req(n 1 , n 2 ) is the co-occurrence frequency of (n 1 , n 2 ) with polarity-identical template pairs (if (n 1 , n 2 ) is PNP) or with polarity-opposite template pairs (if (n 1 , n 2 ) is NNP).
this section shows that our template acquisition method acquired many Excitation templates.