1. A method for optimising a process for a system having a steady-state objective function P(z ∞ ) comprising: producing a minimisation of said steady-state objective function P(z ∞ ) using a computer wherein said minimisation is subject to a set of constraints wherein z min ≦z ∞ ≦z max and wherein values of a state vector, z, at different points in time are related via a model expressed in a dynamic open equation format Q(z ∞ , z k , z k-1 , z k-2 ,. .. , z k-n )=0, where z ∞ is a predicted final value of the state vector, z, and z k , z k-1 , z k-2 ,. .. , z k-n are current and previous values of the state vector, z; and using said minimisation of said steady-state objective function P(z) to control said process via said computer.