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10-703 Homework 1 Programming

Setup

You will need to install the openai gym and numpy in order to complete the assignment. This assignment should work in either python 2.7 or python 3.

We have included a requirements.txt file to make the installation of dependencies easy. We recommend making a virtualenv for this homework. If you are not familiar with virtualenv you can read more about it here: https://virtualenv.pypa.io/en/stable/

You can also install the virtualenvwrapper package if you want a more convenient command line interface.

To install the packages using pip and a virtualenv run the following commands:

virtualenv hw1_env
source hw1_env/bin/activate
pip install -U -r requirements.txt

The following command should now work:

python -c 'import gym'

OpenAI Gym Environments

Creating the environments

To create the environment use the following code snippet:

import gym
import deeprl_hw1.lake_envs

env = gym.make('Deterministic-4x4-FrozenLake-v0')

Actions

There are four actions: LEFT, UP, DOWN, RIGHT represented as integers. The deep_rl_hw1.lake_envs contains variables to reference these. For example:

import deeprl_hw1.lake_envs

print(deeprl_hw1.lake_envs.LEFT)

will print out the number 0.

Environment Attributes

This class contains the following important attributes:

  • nS :: number of states
  • nA :: number of actions
  • P :: transitions, rewards, terminals

The P attribute will be the most important for your implementation of value iteration and policy iteration. This attribute contains the model for the particular map instance. It is a dictionary of dictionary of lists with the following form:

P[s][a] = [(prob, nextstate, reward, is_terminal), ...]

For example, to get the probability of taking action LEFT in state 0 you would use the following code:

import gym
import deeprl_hw1.lake_envs

env = gym.make('Deterministic-4x4-FrozenLake-v0')
state = 0
action = deeprl_hw1.lake_envs.LEFT
print(env.P[state][action])

This will print the list: [(1.0, 0, 0.0, False)] for the Deterministic-4x4-FrozenLake-v0 domain. There is one tuple in the list, so there is only one possible next state.

  • The next state will be state 0 (according to the second number in the tuple) with probability 1.0 (according to the first number in the tuple).
  • The reward for this state-action pair is 0.0 according to the third number.
  • The final tuple value False says that the next state is not terminal.

Sample Code

Running a random policy

See example.py for an example of how to run a random policy in the FrozenLake environment:

python example.py