where m is the molecule, n is a molecule from the training set, N m is the number of atoms in m, the sum i is over all atoms in m, the maximum max j is over all atoms in n, m i is the atomic fingerprint of atom i in m, n h is the fingerprint of atom j in n, and ... 2 represents the L 2 norm. We note that a(m, n) is not a proper distance metric, as a(m, n) = a(n, m).