Method and simulator for real-time calculation of state variables of a process model

A method for real-time calculation of state variables (xM) of a complete process model on a process computer having a first calculating unit and a process interface, wherein the process computer is designed so that at least one state variable (xP) of a physical process is received by the process computer via the process interface and/or at least one output variable (y) is issued by the process computer for controlling the physical process, said method comprising the steps of:

• calculating the complete process model with an explicit integration method by the first calculating unit to determine state variables (xM,e);
• providing a second calculating unit;
• calculating the process model with the second calculating unit using an implicit integration method simultaneously with the calculation of the process model with the first calculating unit, and
• using state variables (xM,i) calculated on the second calculating unit and the implicit method as state variables (xM) of the complete process model if the state variables (xM,i) exist in real time and, if they do not, using the state variables (xM,e) calculated with the explicit integration method as the state variables (xM) of the complete process model,
• said explicit integration method serving as a back-up for calculating the complete process model if the implicit integration method fails to provide the complete process model in real time.