Theory and Practice of
Model-based Reinforcement Learning

Roberto Calandra

Caltech - CS 159 - 25 May 2021

Facebook AI Research

https://slides.com/rcalandra/advances-mbrl/

Towards Artificial Agents in the Wild

Why Robots?

Disaster Relief

Industrial Automation

State of the Art in Robotics

From YouTube: https://www.youtube.com/watch?v=g0TaYhjpOfo

What are we missing?

Key Challenges

• Multi-modal Sensing

• Optimized Hardware Design

• Quick adaptation to new tasks

Hardware

Software

Learning Models of the World for Fast Adaptation of Motor Skills

PILCO [Deisenroth et al. 2011]

Learning Models of the World

Humans seem to make extensive use of predictive models for planning and control *
(e.g., to predict the effects of our actions)

* [Kawato, M. Internal models for motor control and trajectory planning Current Opinion in Neurobiology , 1999, 9, 718 - 727],
   [Gläscher, J.; Daw, N.; Dayan, P. & O'Doherty, J. P. States versus rewards: dissociable neural prediction error signals underlying model-based and model-free reinforcement
    learning Neuron, Elsevier, 2010, 66, 585-595]

Reinforcement Learning Approaches

Model-based Reinforcement Learning

Design Choices in MBRL

• Dynamics Model
  • Forward dynamics
    (Most used nowadays, since it is independent from the task and is causal, therefore allowing proper uncertainty propagation!)
  • What model to use? (Gaussian process, neural network, etc)

• How to compute long-term predictions?
  • Usually, recursive propagation in the state-action space
  • Error compounds multiplicatively
  • How do we propagate uncertainty?

• What planner/policy to use?
  • Training offline parametrized policy
  • or using online Model Predictive Control (MPC)

PILCO [Deisenroth et al. 2011]

• Gaussian Process (GP) for the forward dynamics model
• Propagates uncertainty over state and action by using Moment Matching -- this approximation allows an analytical solution for the derivatives
• Directly optimizes a closed-form policy (e.g., RBF network) by backpropagating the reward through the trajectory to the policy parameters
  (Gradients can be computed easily by chain rule) and using a first-order optimizer.
• Reward function needs to be know in an analytical form

Probabilistic Ensembles with Trajectory Sampling (PETS)

Chua, K.; Calandra, R.; McAllister, R. & Levine, S.
Deep Reinforcement Learning in a Handful of Trials using Probabilistic Dynamics Models
Advances in Neural Information Processing Systems (NIPS), 2018, 4754-4765

Experimental Results

1000x
Faster than
Model-free RL

Chua, K.; Calandra, R.; McAllister, R. & Levine, S.
Deep Reinforcement Learning in a Handful of Trials using Probabilistic Dynamics Models
Advances in Neural Information Processing Systems (NIPS), 2018, 4754-4765

Chua, K.; Calandra, R.; McAllister, R. & Levine, S.
Deep Reinforcement Learning in a Handful of Trials using Probabilistic Dynamics Models
Advances in Neural Information Processing Systems (NIPS), 2018, 4754-4765

Is Something Strange about MBRL?

How to Use the Reward?

Goal-Driven Dynamics Learning

• Instead of optimizing the forward dynamics w.r.t. the NLL of the next state, we optimize w.r.t. the reward
  (The reward is all we care about)
   
• Computing the gradients analytically is intractable
   
• We used a zero-order optimizer: e.g., Bayesian optimization
   
• (and an LQG framework)

Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
Goal-Driven Dynamics Learning via Bayesian Optimization
IEEE Conference on Decision and Control (CDC), 2017, 5168-5173

Real-world Quadcopter

Dubins Car

Not the only way to use the Reward

Bansal, S.; Calandra, R.; Levine, S. & Tomlin, C. J.
MBMF: Model-Based Priors for Model-Free Reinforcement Learning
Withdrawn from Conference on Robot Learning (CORL), 2017

Conclusion

There exist models that are wrong, but nearly optimal when used for control

• From a Sys.ID perspective, they are completely wrong
• These models might be out-of-class (e.g., linear model for non-linear dynamics)
• Hyphothesis: these models capture some structure of the optimal solution, ignoring the rest of the space
• Evidence: these models do not seem to generalize to new tasks

Understand and Overcome the Limitations of MBRL

• Are accurate models condition necessary for good control performance?

• Are accurate models condition sufficient for good control performance?

All models are wrong, but some are useful

- George E.P. Box

If wrong models can be useful,
Can correct models be ineffective?

Objective Mismatch

Model Likelihood vs Episode Reward

Likelihood vs Reward

Deterministic model

Probabilistic model

Assumption: Optimizing the likelihood will optimize the reward

System Identification

Model-based Reinforcement Learning

Sys ID vs MBRL

Objective Mismatch

Experimental results show that the likelihood of the trained models are not strongly correlated with task performance

What are the consequences?

Adversarially Generated Dynamics

What can we do?

• Modify objective when training dynamics model
  • add controllability regularization [Singh et al. 2019]
  • end-to-end differentiable models [Amos et al. 2019]
  • ...
• Move away from the single-task formulation to multi-task
  
• ???

Re-weighted Likelihood

How can we give more importance to data that are important for the specific task at hand?

Re-weighted Likelihood

Understand and Overcome the Limitations of MBRL

• Are accurate models condition necessary for good control performance?

• Are accurate models condition sufficient for good control performance?

• Can we avoid the multiplicative error of recursive one-step predictions?

Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
Goal-Driven Dynamics Learning via Bayesian Optimization
IEEE Conference on Decision and Control (CDC), 2017, 5168-5173

(NO)

1-Step Ahead Models and their Propagation

Trajectory Prediction

Lambert, N.; Wilcox, A.; Zhang, H.; Pister, K. S. J. & Calandra, R.
Learning Accurate Long-term Dynamics for Model-based Reinforcement Learning
Under review, 2020, [available online: https://arxiv.org/abs/2012.09156]

Trajectory Prediction

Results

Lambert, N.; Wilcox, A.; Zhang, H.; Pister, K. S. J. & Calandra, R.
Learning Accurate Long-term Dynamics for Model-based Reinforcement Learning
Under review, 2020, [available online: https://arxiv.org/abs/2012.09156]

Advantages

• Better accuracy for long horizons
• Calibrated uncertainty over the whole trajectory
• Better data efficiency
• Faster computation/propagation for long-horizons
   

(from O(t) to O(1) for any given t)

Understand and Overcome the Limitations of MBRL

• Can we avoid the multiplicative error of recursive one-step predictions?

• Can we dynamically tune the hyperparameters?

• Are accurate models condition necessary for good control performance?

• Are accurate models condition sufficient for good control performance?

Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
Goal-Driven Dynamics Learning via Bayesian Optimization
IEEE Conference on Decision and Control (CDC), 2017, 5168-5173

(NO)

(NO)

Lambert, N.; Amos, B.; Yadan, O. & Calandra, R.
Objective Mismatch in Model-based Reinforcement Learning
Learning for Dynamics and Control (L4DC), 2020, 761-770

Hyperparameters are crucial for MBRL

• MBRL has many hyperparameters that need to be tuned
• Usually manually tuned
• Can we automatize the search for good hyperparameters using AutoML?
• Even more, can we go beyond static hyperparameters?

Example

Results

Results

Conclusion

• Automatically tuning the hyperparameters of MBRL is a really good idea
• Dynamically tuning them is even better
• And conceptually a very interesting thing to do
  (Rejection mechanism for data?)

Understand and Overcome the Limitations of MBRL

• Can we avoid the multiplicative error of recursive one-step predictions?

Lambert, N.; Wilcox, A.; Zhang, H.; Pister, K. S. J. & Calandra, R.
Learning Accurate Long-term Dynamics for Model-based Reinforcement Learning
Under review, 2020, [available online: https://arxiv.org/abs/2012.09156]

(YES)

• Can we dynamically tune the hyperparameters?

• Are accurate models condition necessary for good control performance?

• Are accurate models condition sufficient for good control performance?

Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
Goal-Driven Dynamics Learning via Bayesian Optimization
IEEE Conference on Decision and Control (CDC), 2017, 5168-5173

(NO)

(NO)

Lambert, N.; Amos, B.; Yadan, O. & Calandra, R.
Objective Mismatch in Model-based Reinforcement Learning
Learning for Dynamics and Control (L4DC), 2020, 761-770

A Few Applications

Learning to Fly a Quadcopter

Lambert, N.O.; Drew, D.S.; Yaconelli, J; Calandra, R.; Levine, S.; & Pister, K.S.J.
Low Level Control of a Quadrotor with Deep Model-Based Reinforcement Learning
IEEE Robotics and Automation Letters (RA-L), 2019, 4, 4224-4230

MBRL on Physical Systems

Belkhale, S.; Li, R.; Kahn, G.; McAllister, R.; Calandra, R. & Levine, S.
Model-Based Meta-Reinforcement Learning for Flight with Suspended Payloads

IEEE Robotics and Automation Letters (RA-L), 2021, 6, 1471-1478

Lambeta, M.; Chou, P.-W.; Tian, S.; Yang, B.; Maloon, B.; Most, V. R.; Stroud, D.; Santos, R.; Byagowi, A.; Kammerer, G.; Jayaraman, D. & Calandra, R.
DIGIT: A Novel Design for a Low-Cost Compact High-Resolution Tactile Sensor with Application to In-Hand Manipulation
IEEE Robotics and Automation Letters (RA-L), 2020, 5, 3838-3845

Fine Manipulation using Touch

MBRL in Raw Tactile Space

Lambeta, M.; Chou, P.-W.; Tian, S.; Yang, B.; Maloon, B.; Most, V. R.; Stroud, D.; Santos, R.; Byagowi, A.; Kammerer, G.; Jayaraman, D. & Calandra, R.
DIGIT: A Novel Design for a Low-Cost Compact High-Resolution Tactile Sensor with Application to In-Hand Manipulation
IEEE Robotics and Automation Letters (RA-L), 2020, 5, 3838-3845

Marble Manipulation

Lambeta, M.; Chou, P.-W.; Tian, S.; Yang, B.; Maloon, B.; Most, V. R.; Stroud, D.; Santos, R.; Byagowi, A.; Kammerer, G.; Jayaraman, D. & Calandra, R.
DIGIT: A Novel Design for a Low-Cost Compact High-Resolution Tactile Sensor with Application to In-Hand Manipulation
IEEE Robotics and Automation Letters (RA-L), 2020, 5, 3838-3845

Future Directions

• Better Models
• Better Planning
• Deploying MBRL in the real world can still be daunting
• MBRL from Images
• Beyond 1-step ahead models, towards Hierarchical Planning

A PyTorch Library for MBRL

https://github.com/facebookresearch/mbrl-lib

Pineda, L.; Amos, B.; Zhang, A.; Lambert, N. O. & Calandra, R.
MBRL-Lib: A Modular Library for Model-based Reinforcement Learning
Arxiv, 2021 https://arxiv.org/abs/2104.10159

• Implementing and debugging MBRL algorithms is notoriously difficult
• MBRL-Lib is the first PyTorch library dedicated to MBRL
• Two Goals:
  • High-quality, easy-to-use baselines
  • Framework for quickly implementing and validate new algorithms
• Plan to grow and support this library in the long-term
  • Contributions are welcome!

Human Collaborators

Conclusion

• Model-based RL is a compelling framework for efficiently learn motor skills

  • Orders of magnitude more data-efficient compared to model-free approaches
  • The decision-making process can be analyzed and explained

• Discussed several theoretical and empirical limitations of current approaches

• Many aspects are still poorly understood:
  • What and how to best model the relevant aspects of the world?
  • How to efficiently use these models?
• Our goal is to better understand and improve existing algorithms to make them easier to use and more effective.

• MBRL-Lib is a new open-source library dedicated to MBRL:
  https://github.com/facebookresearch/mbrl-lib

• If you are interested in MBRL, I would be delighted to collaborate.

Backup Slides

References

• Deisenroth, M.; Fox, D. & Rasmussen, C.
  Gaussian Processes for Data-Efficient Learning in Robotics and Control
  IEEE Transactions on Pattern Analysis and Machine Intelligence (PAMI), 2014, 37, 408-423
• Chua, K.; Calandra, R.; McAllister, R. & Levine, S.
  Deep Reinforcement Learning in a Handful of Trials using Probabilistic Dynamics Models
  Advances in Neural Information Processing Systems (NIPS), 2018, 4754-4765
• Tian, S.; Ebert, F.; Jayaraman, D.; Mudigonda, M.; Finn, C.; Calandra, R. & Levine, S.
  Manipulation by Feel: Touch-Based Control with Deep Predictive Models
  IEEE International Conference on Robotics and Automation (ICRA), 2019
• Lambert, N.O.; Drew, D.S.; Yaconelli, J; Calandra, R.; Levine, S.; & Pister, K.S.J.
  Low Level Control of a Quadrotor with Deep Model-Based Reinforcement Learning
  IEEE Robotics and Automation Letters (RA-L), 2019, 4, 4224-4230

• Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
  Goal-Driven Dynamics Learning via Bayesian Optimization
  IEEE Conference on Decision and Control (CDC), 2017, 5168-5173

• Lambert, N.; Amos, B.; Yadan, O. & Calandra, R.

  Objective Mismatch in Model-based Reinforcement Learning
  Under review, Soon on Arxiv, 2019

Ablation Study

Fast and Explainable Adaptation through Model Learning

• Model-based learning algorithms
  • Orders of magnitude more data-efficient compared to model-free approaches
  • The decision-making process can be analyzed and explained
• Many aspects are still poorly understood:
  • what and how to best model the relevant aspects of the world?
  • how to efficiently use these models?
• Our goal is to better understand and improve existing algorithms to make them easier to use and more effective.

References (of our work on model-based RL)

• Belkhale, S.; Li, R.; Kahn, G.; McAllister, R.; Calandra, R. & Levine, S.
  Model-Based Meta-Reinforcement Learning for Flight with Suspended Payloads
  Under review, 2020
• Lambert, N.; Wilcox, A.; Zhang, H.; Pister, K. S. J. & Calandra, R.
  Learning Accurate Long-term Dynamics for Model-based Reinforcement Learning
  Under review, 2020
• Chua, K.; Calandra, R.; McAllister, R. & Levine, S.
  Deep Reinforcement Learning in a Handful of Trials using Probabilistic Dynamics Models
  Advances in Neural Information Processing Systems (NIPS), 2018, 4754-4765
• Lambert, N. O.; Drew, D. S.; Yaconelli, J.; Levine, S.; Calandra, R. & Pister, K. S. J.
  Low Level Control of a Quadrotor with Deep Model-Based Reinforcement Learning
  IEEE Robotics and Automation Letters (RA-L), 2019, 4, 4224-4230
• Lambert, N.; Amos, B.; Yadan, O. & Calandra, R.
  Objective Mismatch in Model-based Reinforcement Learning
  Learning for Dynamics and Control (L4DC), 2020, 761-770
• Bansal, S.; Calandra, R.; Xiao, T.; Levine, S. & Tomlin, C. J.
  Goal-Driven Dynamics Learning via Bayesian Optimization
  IEEE Conference on Decision and Control (CDC), 2017, 5168-5173
• Tian, S.; Ebert, F.; Jayaraman, D.; Mudigonda, M.; Finn, C.; Calandra, R. & Levine, S.
  Manipulation by Feel: Touch-Based Control with Deep Predictive Models
  IEEE International Conference on Robotics and Automation (ICRA), 2019, 818-824
• Lambeta, M.; Chou, P.-W.; Tian, S.; Yang, B.; Maloon, B.; Most, V. R.; Stroud, D.; Santos, R.; Byagowi, A.; Kammerer, G.; Jayaraman, D. & Calandra, R.
  DIGIT: A Novel Design for a Low-Cost Compact High-Resolution Tactile Sensor with Application to In-Hand Manipulation
  IEEE Robotics and Automation Letters (RA-L), 2020, 5, 3838-3845

References

• Yuan, W.; Dong, S. & Adelson, E. H.
  GelSight: High-Resolution Robot Tactile Sensors for Estimating Geometry and Force
  Sensors, 2017
• Calandra, R.; Owens, A.; Jayaraman, D.; Yuan, W.; Lin, J.; Malik, J.; Adelson, E. H. & Levine, S.
  More Than a Feeling: Learning to Grasp and Regrasp using Vision and Touch
  IEEE Robotics and Automation Letters (RA-L), 2018, 3, 3300-3307
• Allen, P. K.; Miller, A. T.; Oh, P. Y. & Leibowitz, B. S.
  Integration of vision, force and tactile sensing for grasping
  Int. J. Intelligent Machines, 1999, 4, 129-149
• Chebotar, Y.; Hausman, K.; Su, Z.; Sukhatme, G. S. & Schaal, S.
  Self-supervised regrasping using spatio-temporal tactile features and reinforcement learning
  International Conference on Intelligent Robots and Systems (IROS), 2016
• Schill, J.; Laaksonen, J.; Przybylski, M.; Kyrki, V.; Asfour, T. & Dillmann, R.
  Learning continuous grasp stability for a humanoid robot hand based on tactile sensing
  BioRob, 2012
• Bekiroglu, Y.; Laaksonen, J.; Jorgensen, J. A.; Kyrki, V. & Kragic, D.
  Assessing grasp stability based on learning and haptic data
  Transactions on Robotics, 2011, 27
• Sommer, N. & Billard, A.
  Multi-contact haptic exploration and grasping with tactile sensors
  Robotics and autonomous systems, 2016, 85, 48-61