We observe that Eq. 3 gives the same quantities as a 1 2 9 i=1 ln λ i , with eigenvalues λ 1 , ..., λ 9 obtained from diagonalizing J T J , where J ∈ R 9×10 is the Jacobian of Eq. 2 given by automatic differentiation. Eq. 3 was therefore evaluated when reconstructing a water molecule, with a negative sign applied to Eq. 3 when mapping a molecule to internal coordinates following the approach described in Ref. .