MultiArmedBandit

This repo contains Ruby code for solving Multi-Armed Bandit problems. This includes the following algorithms:

• Epsilon-Greedy
• Softmax
• Multiple-play Thomson Sampling

Installation

By executing the following line, you can install the gem from RubyGems.

gem install multi_armed_bandit

Usage

Include MultiArmedBandit module by putting the following code.

require 'multi_armed_bandit'
include MultiArmedBandit

Then create an object of Softmax class. The first param is temperature. If we set temperature = 0.0, this will give us deterministic choice of the arm which has highest value. In contrast, if we set temperature = ∞, all actions have nearly the same probability. In a pracitcal sense, temperature tend to be between 0.01 and 1.0.

The second param is number of arms.

sm = MultiArmedBandit::Softmax.new(0.01, 3)

By giving lists of number of trials and rewards to bulk_update method, it returns the predicted probabilities.

# Trial 1
probs = sm.bulk_update([1000,1000,1000], [72,57,49])
counts = probs.map{|p| (p*3000).round }

# Trial 2
probs = sm.bulk_update(counts, [154,17,32])

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

License

The gem is available as open source under the terms of the MIT License.

Reference

[1] John Myles White: Bandit Algorithms for Website Optimization. O'Reilly Media
[2] J. Komiyama, J. Honda, and H.Nakagawa: Optimal Regret Analysis of Thompson Sampling in Stochastic Multi-armed Bandit Problem with Multiple Plays. ICML 2015