As the length of the ground truth sequence is |y * |, the goal of force decoding is to generate a sequence with |y * | words followed by a special end-of-sentence (EOS) symbol.
in beam search, once a candidate translation tends to end with EOS when it is shorter or longer than |y * |, we will force it to generate |y * | words, that is, • If the candidate translation gets a word distribution P j at the j-th step where j |y * | and EOS is the top first word in P j , then we select the top second word in P j as the j-th word of this candidate translation.