Bayesian Optimization
With a surrogate that knows what it does not know, optimization becomes a sequence of decisions: given everything observed so far, where should the next, expensive evaluation go? This part builds the loop that makes those decisions, derives the classic answers to the question, and asks how to tell whether an optimizer is any good.
Acquisition functions are the heart of the part: probability of improvement, expected improvement, upper confidence bounds, Thompson sampling, knowledge gradient, and entropy search, each a different answer to "what is the next observation worth?". Regret and bandits give the theory a vocabulary. The last two chapters leave the textbook for practice: noise, batches, constraints, many dimensions, software, and the fields where Bayesian optimization has paid off.
The part assumes Gaussian process regression (Chapter 8).
Chapters in this part
- 11 The Bayesian Optimization Loop
The problem Bayesian optimization solves, the loop that solves it (fit a surrogate, maximize an acquisition function, evaluate, update), the trade-off between exploring and exploiting that every acquisition function must strike, how to choose the first points, and where the method came from.
- 12 Acquisition Functions
Probability of improvement, expected improvement, upper confidence bounds, Thompson sampling, the knowledge gradient, and entropy search: each a different answer to 'what is the next evaluation worth?', derived and compared on the same posterior in one and two dimensions, followed by how the acquisition function itself is maximized when the domain has many dimensions.
- 13 Regret, Bandits, and Guarantees
How optimizers are scored: simple and cumulative regret, the multi-armed bandit and its classic algorithms, the Lai-Robbins lower bound, GP-UCB's regret bound through the maximum information gain, and what such guarantees do and do not promise in practice.
- 14 Bayesian Optimization in Practice
The decisions a working Bayesian optimization system makes beyond the textbook loop: how to set up the surrogate, what to report under noise, how to choose batches, constraints and safety, several objectives, many dimensions, costs and stopping, and which software implements what.
- 15 Where Bayesian Optimization Works
Hyperparameters, laboratories, robots, engineering designs, online experiments, and people: where Bayesian optimization has paid off and why, and how it relates to its neighbors in active learning, experimental design, bandits, reinforcement learning, and evolution strategies.
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