add discussion on BO on combinatorial spaces

[murphyk]

BO is potentially very useful for optimizing over the space of graphs (eg for molecular design) or strings (eg protein sequences, or ad campaigns). It would great to discuss such discrete domains, beyond R^n.

[bayesoptbook]

Combinatorial domains are discussed at the end of §9.2 (optimization in latent spaces / optimization on combinatorial domains). Graphs (including molecules), set functions, and some general approaches are discussed. I also discuss and some work on protein/gene design in appendix D. Do you have a reference for optimization over strings in an abstract context?

[jungtaekkim]

I think this paper (https://arxiv.org/abs/2010.00979) is a good recent study on Bayesian optimization over strings.

[bayesoptbook]

Thank you @jungtaekkim; I will add the BOSS reference and expand the discussion about optimization over strings specifically (with a pointer to the gene/protein design discussion in appendix D).

[bayesoptbook]

Will appear in the next draft!