, has a value of 1 to specify a perturbation's final state, Δ𝐺 𝑓 , and -1 for the initial state, Δ𝐺 𝑖 , so that ΔΔ𝐺 = Δ𝐺 𝑓 -Δ𝐺 𝑖 ; unconnected ligands have a value of 0. The mapping performed by 𝐀 in Eq. 3 is therefore a graph that defines what ligands (nodes) that transformations (edges) connect. Moreover, 𝐀 is a matrix representation of an unweighted perturbation map. Solving for the error vector, Eq. 3 can be rewritten in the form