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Diffstat (limited to 'dtrain/score.cc')
| -rw-r--r-- | dtrain/score.cc | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/dtrain/score.cc b/dtrain/score.cc new file mode 100644 index 00000000..b09d32ba --- /dev/null +++ b/dtrain/score.cc @@ -0,0 +1,145 @@ +#include "score.h" + +namespace dtrain +{ + + +/* + * bleu + * + * as in "BLEU: a Method for Automatic Evaluation + * of Machine Translation" + * (Papineni et al. '02) + * + * NOTE: 0 if for one n \in {1..N} count is 0 + */ +score_t +BleuScorer::Bleu(NgramCounts& counts, const unsigned hyp_len, const unsigned ref_len) +{ + if (hyp_len == 0 || ref_len == 0) return 0.; + unsigned M = N_; + vector<score_t> v = w_; + if (ref_len < N_) { + M = ref_len; + for (unsigned i = 0; i < M; i++) v[i] = 1./((score_t)M); + } + score_t sum = 0; + for (unsigned i = 0; i < M; i++) { + if (counts.sum_[i] == 0 || counts.clipped_[i] == 0) return 0.; + sum += v[i] * log((score_t)counts.clipped_[i]/counts.sum_[i]); + } + return brevity_penalty(hyp_len, ref_len) * exp(sum); +} + +score_t +BleuScorer::Score(vector<WordID>& hyp, vector<WordID>& ref, + const unsigned /*rank*/, const unsigned /*src_len*/) +{ + unsigned hyp_len = hyp.size(), ref_len = ref.size(); + if (hyp_len == 0 || ref_len == 0) return 0.; + NgramCounts counts = make_ngram_counts(hyp, ref, N_); + return Bleu(counts, hyp_len, ref_len); +} + +/* + * 'stupid' bleu + * + * as in "ORANGE: a Method for Evaluating + * Automatic Evaluation Metrics + * for Machine Translation" + * (Lin & Och '04) + * + * NOTE: 0 iff no 1gram match + */ +score_t +StupidBleuScorer::Score(vector<WordID>& hyp, vector<WordID>& ref, + const unsigned /*rank*/, const unsigned /*src_len*/) +{ + unsigned hyp_len = hyp.size(), ref_len = ref.size(); + if (hyp_len == 0 || ref_len == 0) return 0.; + NgramCounts counts = make_ngram_counts(hyp, ref, N_); + unsigned M = N_; + vector<score_t> v = w_; + if (ref_len < N_) { + M = ref_len; + for (unsigned i = 0; i < M; i++) v[i] = 1./((score_t)M); + } + score_t sum = 0, add = 0; + for (unsigned i = 0; i < M; i++) { + if (i == 0 && (counts.sum_[i] == 0 || counts.clipped_[i] == 0)) return 0.; + if (i == 1) add = 1; + sum += v[i] * log(((score_t)counts.clipped_[i] + add)/((counts.sum_[i] + add))); + } + return brevity_penalty(hyp_len, ref_len) * exp(sum); +} + +/* + * smooth bleu + * + * as in "An End-to-End Discriminative Approach + * to Machine Translation" + * (Liang et al. '06) + * + * NOTE: max is 0.9375 + */ +score_t +SmoothBleuScorer::Score(vector<WordID>& hyp, vector<WordID>& ref, + const unsigned /*rank*/, const unsigned /*src_len*/) +{ + unsigned hyp_len = hyp.size(), ref_len = ref.size(); + if (hyp_len == 0 || ref_len == 0) return 0.; + NgramCounts counts = make_ngram_counts(hyp, ref, N_); + unsigned M = N_; + if (ref_len < N_) M = ref_len; + score_t sum = 0.; + vector<score_t> i_bleu; + for (unsigned i = 0; i < M; i++) i_bleu.push_back(0.); + for (unsigned i = 0; i < M; i++) { + if (counts.sum_[i] == 0 || counts.clipped_[i] == 0) { + break; + } else { + score_t i_ng = log((score_t)counts.clipped_[i]/counts.sum_[i]); + for (unsigned j = i; j < M; j++) { + i_bleu[j] += (1/((score_t)j+1)) * i_ng; + } + } + sum += exp(i_bleu[i])/(pow(2, N_-i)); + } + return brevity_penalty(hyp_len, ref_len) * sum; +} + +/* + * approx. bleu + * + * as in "Online Large-Margin Training of Syntactic + * and Structural Translation Features" + * (Chiang et al. '08) + * + * NOTE: needs some more code in dtrain.cc + */ +score_t +ApproxBleuScorer::Score(vector<WordID>& hyp, vector<WordID>& ref, + const unsigned rank, const unsigned src_len) +{ + unsigned hyp_len = hyp.size(), ref_len = ref.size(); + if (ref_len == 0) return 0.; + score_t score = 0.; + NgramCounts counts(N_); + if (hyp_len > 0) { + counts = make_ngram_counts(hyp, ref, N_); + NgramCounts tmp = glob_onebest_counts_ + counts; + score = Bleu(tmp, hyp_len, ref_len); + } + if (rank == 0) { // 'context of 1best translations' + glob_onebest_counts_ += counts; + glob_onebest_counts_ *= discount_; + glob_hyp_len_ = discount_ * (glob_hyp_len_ + hyp_len); + glob_ref_len_ = discount_ * (glob_ref_len_ + ref_len); + glob_src_len_ = discount_ * (glob_src_len_ + src_len); + } + return (score_t)glob_src_len_ * score; +} + + +} // namespace + |