Written by Blake Milner and Jeff Soldate, with help from Eugenio Culurciello and his lab. Work was done as part of a project for BME495, a Computational Neuroscience course at Purdue. The original code, written in JavaScript, was developed by Andrej Karpathy, a Ph.D. student at Stanford University.
A powerful machine learning algorithm utilizing Q-Learning and Neural Networks, implemented using Torch and Lua.
In many practical engineering scenarios it is often necessary for an algorithm to perform a series of decisions in order to accomplish a given task. However, that task itself is not always well-defined and the intermediate decisions to accomplish it are often complex and ever-changing. Furthermore, information that contributes to accomplishing the task is often not readily available until critical intermediate decisions have already been made. Video games are a good example of situations in which a series of actions is required in order to accomplish a task. In recent years very robust algorithms utilizing these concepts have been developed and applied successfully to retro Atari video games: http://arxiv.org/pdf/1312.5602v1.pdf.
Reinforcement learning methods that encourage both exploration and strategizing have been developed in order to address this problem. One of these methods, called Q-learning, utilizes a policy in order to select an optimal action.
The Q-learning algorithm hinges on utility function called the Q-function. This function accepts a state that contains all pertinent information about the playing field along with a possible action. The function returns a number that describes the utility of that action. In Q-learning the utility of an action is evaluated based on the immediate reward gained from taking that action and the possibility of a delayed reward that the action may lead to. For large games with many states and possible actions the above approach is very time-consuming and computationally intense. Using a neural network to represent the Q-function can solve many of these issues by eliminating the need for enumeration for complete exploration of the state space.
An implementation of the method described above (written in JavaScript) exists and is freely available: http://cs.stanford.edu/people/karpathy/convnetjs/demo/rldemo.html
However, this package is designed for a browser and used primarily as a learning tool. DeepQLearning is a partial port of the Q-learning component of this package to the Lua scripting language. The Neural Network component is powered by Torch 7, a scientific computing framework used for machine learning. It is the hope of the authors that this package can be used to fuel further scientific inquiry into this topic.
Requirements:
- Torch7 (with nnx and optim package) -- A scientific computing framework with wide support for machine learning algorithms. (https://github.com/torch/torch7)
Usage:
The DeepQLearning module can be easily included in a Lua scipt using:
Brain = require 'deepqlearn'The brain must then be initialized with the number of expected inputs and outputs:
Brain.init(num_inputs, num_outputs) An action can be selected from an input state space using:
action = Brain.forward(state); Learning can be effected from the last state space input to Brian.forward by giving a reward value:
Brain.backward(reward);