b19aa25ff58940d974234b48391b9549-Supplemental.pdf

All strings generated by the CFG can be broken down into a (non-unique) tree of production ruleswiththenon-terminal startingsymbolS atitshead. Although each individual production rule is a simplereplacement operation, thecombination ofmanysuchrulescanspecific astringspacewith complex syntactical constraints. However,whensampling strings from the grammar, we found this simple sampling strategy to produce long and repetitive strings. In fact, these tasks are considerably more challenging than the common benchmarks used to test standard BO frameworks. We triedSEkernels withbothindividual andtiedlength scales across latentdimensions, however,this did not have a significant effect on performance, possibly due to difficulties in estimating many kernel parameters inthese low-data BO problems. This ranking matches the relative performance of the BO routines based on these surrogate models (Figure 7). Figure 7.d visualizes the intrinsic representation of an SSK when kernel parameters are purposely chosen to provide a bad fit.