16-745: Optimal Control and Reinforcement Learning
Spring 2020, TT 4:30-5:50 GHC 4303
Instructor: Chris Atkeson, cga@cmu.edu
TA: Ramkumar Natarajan rnataraj@cs.cmu.edu, Office hours Thursdays 6-7 Robolounge NSH 1513

Events of Interest

Items of Interest

DeepMind researchers introduce hybrid solution to robot control problems

Ubisoft Builds New AI Algorithm that Uses Reinforcement Learning to Teach Driving to Itself, another article.

Ancestry turned to AI to bring down cloud costs

Course Description

• Jan 14: Introduction to the course.
  Goal: Introduce course.
  This years emphasis is TBD
  
• Jan 16: AlphaZero/MuZero
  Goal: Introduce you to an impressive example of reinforcement learning (its biggest success). If AI had a Nobel Prize, this work would get it.
  Read MuZero: The triumph of the model-based approach, and the reconciliation of engineering and machine learning approaches to optimal control and reinforcement learning.
• For Jan 30: Read nice reinforcement learning paper:
  Goal: Introduce you to another impressive example of reinforcement learning.
  Read this article, Learning agile and dynamic motor skills for legged robots. Summary video, Just robot abuse video. Running fast video (note asymmetry/"limp"). I have some comments in this article. More comments from me.
• Jan 21: Function Optimization Example
  Goal: Introduce you to a useful tool, MATLAB and its optimization subroutines, and show you how to use them on an example.
  Robotics: redundant inverse kinematics. Using Matlab's fminsearch and fminunc. Using Matlab's fminsearch and fminunc, with desired posture. Using Matlab's fmincon. Relationship of Jacobian approach to gradient descent.
• Jan 23: Handling 3D Orientation
  Goal: Enable you to do 3D robotics using optimization (and do the inverse kinematics assignment).
  Rotation matrices, Euler angles, and Quaternions. Metrics for how close two orientations are: Metrics for 3D Rotations: Comparison and Analysis, Rigid-Body Attitude Control: Using Rotation Matrices for Continuous, Singularity-Free Control Laws, Closed-Loop Manipulator Control Using Quaternion Feedback
  Rotation matrix for small rotations
• Jan 28: Function optimization using first and second order gradient methods
  Goal: Review gradient descent approaches.
  A nice chapter on function optimization techniques: Numerical Recipes in C, chapter 10 (2nd or 3rd edition, 2nd edition is electronically available for free under Obsolete Versions): Minimization or Maximization of Functions, This material from any other numerical methods book is also fine.
  Resources: Matlab fminunc, Numerical Recipes, GSL, AMPL, NEOS, software list 1, Useful software guide, gradient method, line search, conjugate gradient, conjugate gradient v2, quasi-Newton/variable metric methods, Newton's method, Levenberg Marquardt, Reduced dimensionality second order methods.

  Other lectures: Stanford MSandE 311; U. Stuttgart: Toussaint

  Papers: Optimization Methods for Large-Scale Machine Learning; Identifying and attacking the saddle point problem in high-dimensional non-convex optimization

• Talk about Covariant roll-out.
• Talk about robot example: Learning agile and dynamic motor skills for legged robots.
• Jan 30: Non-gradient ("derivative-free") function optimization methods:
  Goal: Review non-gradient approaches.
  hill climbing (including local search, local unimodal sampling, pattern search, random search, random optimization), Nelder Mead/Simplex/Amoeba method, Matlab fminsearch, simulated annealing, fit surfaces (for example Response Surface Methodology (RSM), Memory-based Stochastic Optimization, and Q2), evolutionary algorithms, genetic algorithms, and ...
  Paper: Derivative-free optimization: A review of algorithms and comparison of software implementations by Luis Miguel Rios and Nikolaos V. Sahinidis, Book: Introduction to Derivative-Free Optimization
• Jan 30: Covariance Matrix Adaptation Evolution Strategy.
  Goal: Understand currently popular state of the art method.
  See also Hansen web page. Example1, Ex2, Ex3, Ex4.
  
• Feb 4: Constraints.
  Goal: Understand how to handle constraints.
  Soft/hard constraints, penalty functions, Barrier functions, Lagrange Multipliers, Karush-Kuhn-Tucker conditions, Slack variables, Augmented Lagrangian method, Interior point methods vs. Simplex methods vs. soft constraint methods.
• Feb 4: Quadratic Programming and Sequential quadratic programming,
  Goal: Understand QP components used in state of the art robot control.
  Matlab fmincon. SNOPT, CVXGEN, IPOPT
• Feb 4: Dynamics and Numerical Integration
  Goal: Review "mental practice".
  Continuous time dynamics, discrete time dynamics. Euler integration, Forward and inverse dynamics. Linearization.
• Feb 6: Formulating trajectory optimization as function optimization.
  Goal: Use the tools we have so far to do trajectory optimization.
  Examples of formulating a trajectory optimization problem as a function optimization problem: Case Studies In Trajectory Optimization: Trains, Planes, And Other Pastimes, Robert J. Vanderbei
  Example use of AMPL
  A free trial version of AMPL is available from here.
  AMPL is also available for remote use through the Neos Server. Click on SNOPT/[AMPL Input] under Nonlinearly Constrained Optimization.
  Example use of Matlab: pend1-x-u, pend1-u, pend1-x
  Spacetime Optimization: Witkin paper text Witkin paper figures
  
• Feb 6: Use of splines in trajectory optimization.
  Goal: Force smooth solutions.
  Cubic Hermite spline. Quintic Hermite interpolation.
  Collocation, Pseudospectral X.
  Wavelets
• Feb 11: Policy optimization I: Use function optimization.
  Goal: Optimize feedback.
  What is a policy? Known in machine learning/reinforcement learning as policy search or refinement, ...
  slides See examples in CMA-ES section for policy optimization.
• Feb 11: Ways to robustify function optimization:
  Goal: Tricks of the trade.
  Problems: How choose method?, more of an art than a science, local minima, bad answers, discontinuities, redundant/rank deficient constraints, bad scaling, no formulas for derivatives, you are lazy, computational cost.
  Techniques: Levenberg Marquardt, Trust regions, line search, scaling and preconditioning, regularize parameters, soft constraints, sparse methods, Continuation Methods, Paper on continuation methods, Hand of God, allow constraint violations, add extra constraints, use multiple starts, use multiple methods, optimize meta-parameters (learn to learn)
  Matlab recommendations for optimization, more, more, global optimization, more
• Feb 13: Dynamic Programming.
  Goal: Use of value function is what makes optimal control special.
  Bellman equation,
  slides
• Feb 18: Linear Quadratic Regulator,
  Goal: An important special case.
  Riccati Equation, Differential Dynamic Programming
• Feb 20: Ways to reduce the curse of dimensionality
  Goal: Tricks of the trade.
  slides
• Policy Optimization II: Optimization using model-based gradients
  Goal: The Chain Rule Is Powerful.
  slides
• Robustness
  Goal: How To Handle Bad Models.
  Robustness to random disturbances, varying initial conditions, parametric model error, structural modeling error such as high frequency unmodelled dynamics, and model jumps (touchdown and liftoff during walking, for example). Monte Carlo trajectory/policy optimization. Monte carlo financial planning.
• Robustness using Linear Matrix Inequalities
  Goal: Handling Parametric Uncertainty.
  Robustness to parametric uncertainty in the linear(ized) model. Tutorial on LMIs, Slides: Continuous time stability slide 47, Discrete time stability slide 51
• Receding Horizon Control (a.k.a. Model Predictive Control (MPC))
  Goal: Online Optimization.
  
• Robustness: Policy Optimization with Multiple Models.
  Goal: A powerful tool to handle all kinds of uncertainty.
  Monte-Carlo, DP, and DDP approaches to Multiple Models.
• Bayesian Filters
  Goal: Explicitly model uncertainty.
  State Estimation, Uncertainty Propagation: Gaussian Propagation (like Kalman Filter), Unscented (like Unscented Filter), Second Order Kalman Filter (See Kendrick below).
  Review of Gaussians slides
  State estimation slides
  Matlab Kalman filter example and minimum jerk trajectory subroutine.
  Example mobile robot Kalman filter slides
  
• Robustness and state estimation:
  Goal: How to combine state estimation and control.
  Linear-quadratic-Gaussian control (LQG), Separation principle, Certainty equivalence, Example of bad interactions, Loop Transfer Recovery (LTR), A paper on the topic, Policy optimization approaches.
• Dual Control. Simple example. Information state DP.
• Local Approaches to Dual Control/Stochastic DDP Information state trajectory optimization. Stochastic Control for Economic Models, David Kendrick, Second Edition 2002.
• A*-like algorithms: R*
• Avoiding obstacles using sampling-based methods: RRT, slides Projected RRT, RRT* slides video 1 video 2 LQR-RRT* Random Sampling DP
• Avoiding obstacles using gradient methods: CHOMP STOMP
• Learning From Demonstration
• Reinforcement Learning: Model free policy gradient. Use trajectories to determine outcomes. Kober, J.; Peters, J. (2011). Policy Search for Motor Primitives in Robotics, Machine Learning, 84, 1-2, pp.171-203
  NIPS Tutorial 2016: Deep Reinforcement Learning Through Policy Optimization
  10-703 lecture notes I Proximal Policy Optimization
• Reinforcement Learning: Model free actor-critic: Model Q function to determine outcomes. 10-703 lecture notes II Continuous control with deep reinforcement learning
• What's new (2018 version)?
  • Emergence of Locomotion Behaviours in Rich Environments video
• Comparison of various RL methods Freek Stulp and Olivier Sigaud. Path Integral Policy Improvement with Covariance Matrix Adaptation. In Proceedings of the 29th International Conference on Machine Learning (ICML), 2012.
  Linear policies work: Towards Generalization and Simplicity in Continuous Control
  Simple random search provides a competitive approach to reinforcement learning
  Simple Nearest Neighbor Policy Method for Continuous Control Tasks, reddit commentary
  Neural Network Dynamics for Model-Based Deep Reinforcement Learning with Model-Free Fine-Tuning
  Deep Reinforcement Learning for Dexterous Manipulation with Concept Networks
  Evolution Strategies as a Scalable Alternative to Reinforcement Learning
  
• Inverse Reinforcement Learning. Abbeel slides Finn slides 10-703 lecture
• What's new (2017 version)?
  • Combine trajectory optimization (model-based) and policy learning (model-free). I did some work on this 20+ years ago. Now it is coming back.
    Robot Learning From Demonstration, ICML '97, (postscript),
    Learning tasks from a single demonstration, ICRA '97,
    Nonparametric Model-Based Reinforcement Learning, NIPS '97,
    Using Local Trajectory Optimizers To Speed Up Global Optimization in Dynamic Programming, NIPS 93
    Random Sampling of States in Dynamic Programming, Trans SMC, 2008
    Combining Model-Based and Model-Free Updates for Trajectory-Centric Reinforcement Learning
    
  • Create primitives and learn to combine them. (Libin Liu).
    Akihiko Yamaguchi
    Google semantic event chains
    Freek Stulp
    Karinne Ramirez-Amaro
    another Cheng paper
    
  • What did the Berkeley folks say?
    See second half of Sergey Levine's lecture
    Finn's lecture on Transfer, Learning to Learn
    See last slide of Abbeel's lecture
    
• Review of Traditional Approaches Trajectory optimization based on integrating the dynamics: calculus of variations, Euler-Lagrange equation, Discrete time Pontryagin's minimum principle, Pontryagin's minimum principle, Hamilton-Jacobi-Bellman equation, costate equations, shooting methods, multiple shooting methods, Karush-Kuhn-Tucker conditions Continuation Methods, Meta-optimization, Learning during optimization
• Automatic differentiation
  Goal: Learn how taking derivatives is much easier than you thought.
  
• Gaussian Process Optimization.
  Goal: The role of knowledge in optimization.
  When solving the same kind of problem many times: Learn about the function: remember previous answers, bases of attraction, features like saddle points (zero gradients), optimization paths, ... Learn about which optimization method works best: Meta-optimization. Assume or learn a structure for the function (kernel in GP is an example).
• Finding Better Ways To Do Task
  Goal: Think about an important current research problem.
  
• ...
• April 28 & 30: Project presentations
• May 17 (May 12 for graduating students): Final project writeup (web page) due.

Assignments

• Assignment 0 (Due Jan. 20): Send CGA and TA email: Who are you? Why are you here? What research do you do? Describe any optimization you have done (point me to papers or web pages if they exist). Any project ideas? What topics would you especially like the course to cover?
  Be sure your name is obvious in the email, and you mention the course name or number. I teach more than one course, and a random email from robotlover@cs.cmu.edu is hard for me to process.
• Assignment 1 (Due Jan 27): Using Optimization to do Inverse Kinematics

Project

Project suggestions