BUG correct beam_width upper bound #192
Description
The current beam search algorithm has the following properties.
- In each iteration, different beams cannot select the same feature;
- while the different beams can select the same features in different iterations.
These properties take care of both the width and the depth of exploration.
In this beam search algorithm, beam_width can equal the number of features. In addition, the number of features to select does not affect beam_width. It is even possible to make both beam_width and n_features_to_select equal to n_features.