Then each character c ∈ C is mapped into an ddimensional embedding space as c ∈ For each character c i in a given sentence c 1:n , the context characters c i−w 1 :i+w2 are mapped to their corresponding character embeddings as c i−w 1 :i+w 2 , where w 1 and w 2 are left and right context lengths respectively.
the unknown characters and characters exceeding the sentence boundaries are mapped to special symbols, "unknown", "start" and "end" respectively.