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Curse of dimensionality

As explained in Bayesian Optimization in Action

The curse of dimensionality is the phenomenon in which computational or statistical costs grow exponentially as the number of dimensions increases.

The curse of dimensionality describes how many machine-learning procedures become exponentially more expensive as the dimensionality of the object of interest increases. In Bayesian optimization, estimating the distribution of an objective function’s optimizer requires exponentially more samples as the input vector grows. section 6.2.1 section 6.4

Optimizer location versus optimal value

Entropy search tries to model the optimizer x*, the input location where the objective reaches its maximum. Its distribution is complicated and increasingly costly to approximate in higher dimensions. A practical alternative targets the optimal value f* = f(x*), which is always one-dimensional; Max-value Entropy Search uses this reformulation to reduce the burden. section 6.2.1 section 6.4

Figure 6.11 The GP belief (top left), the distribution of the function optimizer x* (bottom), and the distribution of the optimal value f* (right). The distribution of the optimal value is always one-dimensional and, therefore, easier to work with than that of the optimizer.

Compare the complicated distribution of the optimizer x* with the one-dimensional distribution of the optimal value f*. section 6.2.1

How Bayesian Optimization in Action covers it

How deep it goes
Defines exponential cost and explains its effect on Gaussian-process sampling, stopping short of general complexity analysis.
Examples
Uses optimizer-location sampling and contrasts it with the one-dimensional optimal-value distribution.
What it assumes
Assumes familiarity with objective functions and Bayesian optimization while introducing the dimensionality-cost relationship directly.
What you can do after
Diagnose dimensionality bottlenecks and understand why targeting the optimal value enables a more tractable BayesOpt policy.
How it connects
Connects entropy search, Bayesian optimization, Gaussian processes, optimal values, and Max-value Entropy Search.

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