# Creating a New Policy¶

This tutorial describes the standard RLPy Policy interface, and illustrates a brief example of creating a new problem domain.

The Policy determines the discrete action that an Agent will take given its current value function Representation.

The Agent learns about the Domain as the two interact. At each step, the Agent passes information about its current state to the Policy; the Policy uses this to decide what discrete action the Agent should perform next (see pi()) n

Warning

While each dimension of the state s is either continuous or discrete, discrete dimensions are assume to take nonnegative integer values (ie, the index of the discrete state).

Note

You may want to review the namespace / inheritance / scoping rules in Python.

## Requirements¶

• Each Policy must be a subclass of Policy and call the __init__() function of the Policy superclass.
• Any randomization that occurs at object construction MUST occur in the init_randomization() function, which can be called by __init__().
• Any random calls should use self.random_state, not random() or np.random(), as this will ensure consistent seeded results during experiments.
• After your Policy is complete, you should define a unit test to ensure future revisions do not alter behavior. See rlpy/tests for some examples.

### REQUIRED Functions¶

1. pi() - accepts the current state s, whether or not s is terminal, and an array of possible actions indices p_actions and returns an action index for the Agent to take.

### SPECIAL Functions¶

Policies which have an explicit exploratory component (eg epsilon-greedy) MUST override the functions below to prevent exploratory behavior when evaluating the policy (which would skew results)

1. turnOffExploration()
2. turnOnExploration()

• As always, the Policy can log messages using self.logger.info(<str>), see Python logger documentation.
• You should log values assigned to custom parameters when __init__() is called.
• See Policy for functions provided by the superclass.

## Example: Creating the Epsilon-Greedy Policy¶

In this example we will recreate the eGreedy Policy. From a given state, it selects the action with the highest expected value (greedy with respect to value function), but with some probability epsilon, takes a random action instead. This explicitly balances the exploration/exploitation tradeoff, and ensures that in the limit of infinite samples, the agent will have explored the entire domain.

1. Create a new file in your current working directory, eGreedyTut.py. Add the header block at the top:

__copyright__ = "Copyright 2013, RLPy http://www.acl.mit.edu/RLPy"
__credits__ = ["Alborz Geramifard", "Robert H. Klein", "Christoph Dann",
"William Dabney", "Jonathan P. How"]
__author__ = "Ray N. Forcement"

from rlpy.Policies.Policy import Policy
import numpy as np

2. Declare the class, create needed members variables, and write a docstring description. See the role of member variables in comments:

class eGreedyTut(Policy):
"""
From the tutorial in policy creation.  Identical to eGreedy.py.
"""

# Probability of selecting a random action instead of greedy
epsilon         = None
# Temporarily stores value of epsilon when exploration disabled
old_epsilon     = None
# bool, used to avoid random selection among actions with the same values
forcedDeterministicAmongBestActions = None

3. Copy the __init__() declaration from Policy.py and add needed parameters. In the function body, assign them and log them. Then call the superclass constructor. Here the parameters are the probability of selecting a random action, epsilon, and how to handle the case where multiple best actions exist, ie with the same value, forcedDeterministicAmongBestActions:

def __init__(self,representation, epsilon = .1,
forcedDeterministicAmongBestActions = False, seed=1):
self.epsilon = epsilon
self.forcedDeterministicAmongBestActions = forcedDeterministicAmongBestActions
super(eGreedyTut,self).__init__(representation)

4. Copy the pi() declaration from Policy.py and implement it to return an action index for any given state and possible action inputs. Here, with probability epsilon, take a random action among the possible. Otherwise, pick an action with the highest expected value (depending on self.forcedDeterministicAmongBestActions, either pick randomly from among the best actions or always select the one with lowest index:

def pi(self,s, terminal, p_actions):
coin = self.random_state.rand()
#print "coin=",coin
if coin < self.epsilon:
return self.random_state.choice(p_actions)
else:
b_actions = self.representation.bestActions(s, terminal, p_actions)
if self.forcedDeterministicAmongBestActions:
return b_actions[0]
else:
return self.random_state.choice(b_actions)

5. Because this policy has an exploratory component, we must override the turnOffExploration() and turnOnExploration() functions, so that when evaluating the policy’s performance the exploratory component may be automatically disabled so as not to influence results:

def turnOffExploration(self):
self.old_epsilon = self.epsilon
self.epsilon = 0
def turnOnExploration(self):
self.epsilon = self.old_epsilon


Warning

If you fail to define turnOffExploration() and turnOnExploration() for functions with exploratory components, measured algorithm performance will be worse, since exploratory actions by definition are suboptimal based on the current model.

That’s it! Now test your new Policy by creating a simple settings file on the domain of your choice. An example experiment is given below:

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 #!/usr/bin/env python """ Policy Tutorial for RLPy ================================= Assumes you have created the eGreedyTut.py agent according to the tutorial and placed it in the current working directory. Tests the policy on the GridWorld domain, with the policy and value function visualized. """ __author__ = "Robert H. Klein" from rlpy.Domains import GridWorld from rlpy.Agents import SARSA from rlpy.Representations import Tabular from eGreedyTut import eGreedyTut from rlpy.Experiments import Experiment import os def make_experiment(exp_id=1, path="./Results/Tutorial/gridworld-eGreedyTut"): """ Each file specifying an experimental setup should contain a make_experiment function which returns an instance of the Experiment class with everything set up. @param id: number used to seed the random number generators @param path: output directory where logs and results are stored """ opt = {} opt["exp_id"] = exp_id opt["path"] = path ## Domain: maze = '4x5.txt' domain = GridWorld(maze, noise=0.3) opt["domain"] = domain ## Representation # discretization only needed for continuous state spaces, discarded otherwise representation = Tabular(domain, discretization=20) ## Policy policy = eGreedyTut(representation, epsilon=0.2) ## Agent opt["agent"] = SARSA(representation=representation, policy=policy, discount_factor=domain.discount_factor, initial_learn_rate=0.1) opt["checks_per_policy"] = 100 opt["max_steps"] = 2000 opt["num_policy_checks"] = 10 experiment = Experiment(**opt) return experiment if __name__ == '__main__': experiment = make_experiment(1) experiment.run(visualize_steps=False, # should each learning step be shown? visualize_learning=True, # show policy / value function? visualize_performance=1) # show performance runs? experiment.plot() experiment.save() 

## What to do next?¶

In this Policy tutorial, we have seen how to

• Write a Policy that inherits from the RLPy base Policy class
• Override several base functions, including those that manage exploration/exploitation
• Add the Policy to RLPy and test it

If you would like to add your component to RLPy, we recommend developing on the development version (see Development Version). Please use the following header at the top of each file:

__copyright__ = "Copyright 2013, RLPy http://www.acl.mit.edu/RLPy"
__credits__ = ["Alborz Geramifard", "Robert H. Klein", "Christoph Dann",
"William Dabney", "Jonathan P. How"]

• Fill in the appropriate __author__ name and __credits__ as needed. Note that RLPy requires the BSD 3-Clause license.
• If you installed RLPy in a writeable directory, the className of the new policy can be added to the __init__.py file in the Policies/ directory. (This allows other files to import the new policy).
You can also email the community list rlpy@mit.edu for comments or questions. To subscribe click here.