Abstractions, algorithms, and utilities for reinforcement learning in Julia



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Reinforce.jl is an interface for Reinforcement Learning. It is intended to connect modular environments, policies, and solvers with a simple interface.

Packages which build on Reinforce:

Environment Interface

New environments are created by subtyping AbstractEnvironment and implementing a few methods:

  • reset!(env) -> env
  • actions(env, s) -> A
  • step!(env, s, a) -> (r, s′)
  • finished(env, s′) -> Bool

and optional overrides:

  • state(env) -> s
  • reward(env) -> r

which map to env.state and env.reward respectively when unset.

  • ismdp(env) -> Bool

An environment may be fully observable (MDP) or partially observable (POMDP). In the case of a partially observable environment, the state s is really an observation o. To maintain consistency, we call everything a state, and assume that an environment is free to maintain additional (unobserved) internal state. The ismdp query returns true when the environment is MDP, and false otherwise.

  • maxsteps(env) -> Int

The terminating condition of an episode is control by maxsteps() || finished(). It's default value is 0, indicates unlimited.

An minimal example for testing purpose is test/foo.jl.

TODO: more details and examples

Policy Interface

Agents/policies are created by subtyping AbstractPolicy and implementing action. The built-in random policy is a short example:

struct RandomPolicy <: AbstractPolicy end
action(π::RandomPolicy, r, s, A) = rand(A)

Where A is the action space. The action method maps the last reward and current state to the next chosen action: (r, s) -> a.

  • reset!(π::AbstractPolicy) -> π

Episode Iterator

Iterate through episodes using the Episode iterator. A 4-tuple (s,a,r,s′) is returned from each step of the episode:

ep = Episode(env, π)
for (s, a, r, s′) in ep
    # do some custom processing of the sars-tuple
R = ep.total_reward
T = ep.niter

There is also a convenience method run_episode. The following is an equivalent method to the last example:

R = run_episode(env, π) do
    # anything you want... this section is called after each step

Author: Tom Breloff

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