Fixed-length random walk graph kernel. We used MolecularGraph.jl to obtain the molecular graphs {G 1 , ..., G N } representing the pesticide molecules. For each pair of graphs (G i , G j ), we constructed their direct product graph G i × G j , evaluated the L-RWGK k (L) (G i , G j ) via eqn. 11 (using our own code), then stored it in a Gram matrix K (L) , for L ∈ {0, ..., 12}.