“…This results in the simulation errors not only for upstream outputs but also for downstream outputs, since the upstream variables affects the downstream variables directly, and vice versa. When (18) is used as the model structure to predict the output of the downstream variable, such nonlinearities in the upstream is detected by the upstream sensor or transmitter, and is used as one of the model inputs. In the same way, when (17) is used to predict the upstream variable, such nonlinearities affects first the downstream variable, then is detected by downstream sensor or transmitter, and further be used as one of the model inputs.…”