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Q-Learning a Car to Drive on a Narrow Track

This is the code behind https://youtu.be/o7VYaKHq9jw, Q-learning: car driving narrow track (4). Model building blocks

The code is provided as per request in the youtube comments section.

System requirements

  • Simulation: Python 2.7 or Python 3. Use of PyPy or PyPy3 implementation is strongly recommended. No external dependencies.
  • Plotting: Python 2.7 or Python 3, numpy, matplotlib. (known limitation: it appears that generating mp4 files of the animation may not work reliably under Python 3.6 with matplotlib 2.x. It seems to work fine under Python 2.7 with matplotlib 1.x.)

Overview

A Q-learner has been implemented in Python with the Q-function stored in a table. The problem has been split into three elements:

  1. A physical model of the world
  2. An interface layer between the world and the numerical Q-learner
  3. The numerical Q-learner

The flow of information is illustrated in this diagram: Model building blocks

The individual building blocks of the simulation are implemented in the following modules:

  • Current Model State: Part of the main loop in system.py
  • Process Model: a1_process_model.py
  • Reward Function: a2_reward_system.py
  • Environment State: a3_environment_context.py
  • Observer/Actor: b_observer.py
  • Q-learner: c_q_learner.py

In addition,

  • Track generator: Routines for generating the train tracks (simulation) and the test track (plotting) are in track_generator.py.
  • Helper functions: for the physical model of the world geometry.py
  • Input/Output save_load.py imports or exports learned data as json

Exported simulations can be visualized with

  • Plotting show.py

A learned model is provided as data/learned_result_11040091.json (based on 11,040,091 iterations), which has been used to generate data/sample_run_11040091.mp4 (i.e. the same simulation seen on youtube).

Program Flow

The main loop in system.py is approximately

model_state = process_model.ModelState(position, rotation, wheel_direction, car_speed, 0., None)
while model_state.status != 'terminated':
    numerical_state = observer.state_for_learner(model_state)
    numerical_action = q_learner.policy(numerical_state, epsilon=epsilon)
    model_action = observer.action_for_model(model_state, numerical_state, numerical_action)
    new_model_state = model.act(model_state, model_action)
    model_reward = reward.reward(model_state, model_action, new_model_state)
    new_numerical_state = observer.state_for_learner(new_model_state)
    numerical_reward = observer.reward_for_learner(model_reward)
    q_learner.learn(numerical_state, numerical_action, numerical_reward, new_numerical_state, alpha=alpha)
    model_state = new_model_state

Installation

Copy all files of the src directory to a local directory. To use the simulation results provided, copy json data from data/ into the same directory.

Execution

Simulation

To start learning from a blank slate, run pypy system.py or pypy3 system.py. The standard CPython implementations can be used for testing but run too slow to be of practical use. Learned data are written to the current directory in regular intervals.

Plotting

To generate an animation from the learned data run python show.py or python3 show.py. The latest simulation data in the current directory will be used for plotting (based on filename).

License

MIT