“…This procedure is longer and more difficult to pursue, as in principle many possible regressor combinations in the regressor pool must be tested. Based on the prior process knowledge from [23] and its authors, the following regressors were chosen for the initial GP model structure: [S 1,2,3 out S 4 in T 2 DO 3 1 DO 1 2 ], where the superscript denotes the delay, e.g. S 4 in = S in (k − 4).…”