 A final modification to the SHAKE algorithm is the P-SHAKE algorithm that is applied to very rigid or semi-rigid molecules.P-SHAKE computes and updates a pre-conditioner which is applied to the constraint gradients before the SHAKE iteration, causing the Jacobian formula_21 to become diagonal or strongly diagonally dominant.The thus de-coupled constraints converge much faster (quadratically as opposed to linearly) at a cost of formula_47.