GitLab

Summary:
Implement Nucleus (top-P) sampling: sample among the smallest set of elements whose cumulative probability mass exceeds p.

To test it:
python generate.py   ~myleott/data/data-bin/wmt17_zh_en_full/   --path ~myleott/zh_en/model.pt   --remove-bpe   --nbest 5   --beam 5 --sampling --sampling-topp 0.3
Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/710

Test Plan:
python generate.py   ~myleott/data/data-bin/wmt17_zh_en_full/   --path ~myleott/zh_en/model.pt   --remove-bpe   --nbest 5   --beam 5 --sampling --sampling-topp 0.3

python tests/test_sequence_generator.py

python tests/test_binaries.py

Reviewed By: myleott

Differential Revision: D16286688

Pulled By: xingz9

fbshipit-source-id: 1776d21e17c4532a3d24ac75bb7e75da9acad58f