What is length penalty in beam search?
The length penalty is a methodology that prevents the probability value from decreasing when a long sentence is translated. The cumulative probability is eventually calculated during the beam search, and it ranges from 0 to 1.
What is beam size in beam search?
In the “standard” beam search algorithm, at every step, the total number of the nodes you currently “know about” is limited – and NOT the number of nodes you will follow from each node. Concretely, if n = 2 , it means that the “beam” will be of size at most 2, at all times.
What is beam width in beam search algorithm?
Beam search uses breadth-first search to build its search tree. At each level of the tree, it generates all successors of the states at the current level, sorting them in increasing order of heuristic cost. However, it only stores a predetermined number, , of best states at each level (called the beam width).
How the beam width will affect the performance of the beam search?
Larger beam widths result in better performance of a model as the multiple candidate sequences increase the likelihood of better matching a target sequence. This increased performance results in a decrease in decoding speed. At each step, each candidate sequence is expanded with all possible next steps.
Should BLEU score be high or low?
Interpretation
| BLEU Score | Interpretation |
|---|---|
| 30 – 40 | Understandable to good translations |
| 40 – 50 | High quality translations |
| 50 – 60 | Very high quality, adequate, and fluent translations |
| > 60 | Quality often better than human |
What’s the default beam size in beam search?
The small default beam size is often enough in practice. Beam search can also be used to provide an approximate n-best list of translations by setting -n_best greater than 1. For analysis, the translation command also takes an oracle/gold -tgt file and will output a comparison of scores.
What can beam search be used for in OpenNMT?
The beam search also supports various normalization techniques that are disabled by default and can be used to biased the scores generated by the model: where X is the source, Y is the current target, and the functions as defined below. An additional penalty on end of sentence tokens can also be added to prioritize longer sentences.
Can a beam search be constrained to produce a translation?
Beam search can be constrained to produce translations from a phrase table in its output, whenever corresponding source tokens are found on the input side. The implementation is based on the Grid Beam Search approach described in Hokamp and Liu (2017) . For the moment, only simple one-token constraints are accepted.
How to use shallow fusion in beam search?
Beam search can use an additional language model to modify score of each option as defined in Gulcehre et al. (2015) as “Shallow Fusion”: Where s L M ( Y) is the language model log-probability of the sequence Y and β is defined by -lm_weight parameter. To activate the language model, simply use -lm_model lm.t7.