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Safe Reinforcement Learning Algorithms



HCOPE (High-Confidence Off-Policy Evaluation.)

Python Implementation of HCOPE lower bound evaluation as given in the paper: Thomas, Philip S., Georgios Theocharous, and Mohammad Ghavamzadeh. "High-Confidence Off-Policy Evaluation." AAAI. 2015.

CUT Inequality

Requirements

  • PyTorch
  • Numpy
  • Matplotlib
  • scipy
  • gym

Running Instructions

  1. Modify the environment in the main function, choosing from OpenAI gym. (Currently the code works for discrete action spaces)
  2. Run python hcope.py

Notes

  • The file policies.py contains the policy used in the code. Modify the policy to suit your needs in this file.
  • To reproduce the graph given in the original paper explaining the long tail problem of importance sampling, use the
visualize_IS_distribution()

method. Also, a graph of distribution of Importance sampling ratio is created which nicely explains the high variance of the simple IS estimator. Variance in simple IS

  • All the values required for offpolicy estimation are initialized in the HCOPE class initialization.

  • Currently the estimator policy is defined as a gaussian noise(mean,std_dev) added to the behavior policy for estimator policy initialization in the function setup_e_policy(). The example in paper uses policies differing by natural gradient. But, this works as well.

  • To estimate c*, I use the BFGS method which does not require computing hessian or first order derivative.

  • The hcope_estimator() method also implements a sanity check, by computing the discriminant of the quadratic in parameter delta(confidence). If it does not satisfy the basic constraints, the program prints the bound predicted is of zero confidence.

  • The random variables are implemented using simple importance sampling. Per-decision importance sampling might lead to better bounds and is to be explored.

  • A bilayer MLP policy is used for general problems.

  • Results:
    Output format: Output


Safe exploration in continuous action spaces.

Paper: Safe Exploration in Continuous Action Spaces - Dalal et al.

Running Instructions

  • Go inside safe_exploration folder
  • First learn the safety function by collecting experiences
    python learn_safety_function.py
  • Now using the learned safety function, add the path of these learned torch weights in the train_safe_explorer.py file. After that:
    python train_safe_explorer.py
    This enables agent to learn while following the safety constraints.

Results

  • Safe exploration in a case where constraint is on crossing the right lane marker.

Safe Exploration

  • Instability is observed in safe exploration using this method. Here constraint is activated going left through the center of the road.(0.3)

Unstability due to Safe Exploration

Explanation

  • Linear Safety Signal Model

Safety Signal

  • Safety Layer via Analytical Optimization

Safety Layer

  • Action Correction

Action Correction


Importance Sampling

Implementation of:

  • Simple Importance Sampling
  • Per-Decision Importance Sampling
  • Normalized Per-Decision Importance Sampling (NPDIS) Estimator
  • Weighted Importance Sampling (WIS) Estimator
  • Weighted Per-Decision Importance Sampling (WPDIS) Estimator
  • Consistent Weighted Per-Decision Importance Sampling (CWPDIS) Estimator

Comparision of different importance sampling estimators:
Different Importance sampling estimators

Image is taken from phD thesis of P.Thomas:
Links: https://people.cs.umass.edu/~pthomas/papers/Thomas2015c.pdf


Side Effects

Penalizing side effects using relative reachability

Code - https://github.com/hari-sikchi/safeRL/tree/safe_recovery/side_effects

  • Added a simple example for calculating side effects as given towards the end of paper Environment

The relative reachability measure
Equation relative reachability

Paper: Penalizing side effects using stepwise relative reachability - Krakovna et al.

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