GSP models > States and errors > Controlling states and errors

A GSP model equation may be replaced by a dummy equation if the actual equation is deactivated (e.g. by unchecking the Active field in the General tab sheet of a controller component). The dummy equation must depend on at least one state variable in order to prevent a singular Jacobian matrix that cannot be inverted. This means the dummy equation needs a corresponding state (that has to be dummy as well) and not controlled anymore by the iteration solving the set of equations. The corresponding state often is user specified. As such this state variable is not connected to the internal model parameter (such as a rotor speed or something else) but simply used to form a dummy error equation of the form Error = State-1. This results in the particular dummy state to become equal to 1 and the error equal to 0 upon convergence without interfering with the engine model equations.