x is an m-dimensional row vector representing the regressors and r is the mean of the regressors x. To understand the structure of nonlinear ARX models, refer to pages 11-18 to 11-19 of the following documentation:
Refer to pages 11-63 to 11-64 of the above documentation for an example that preforms a low-level computation of the nonlinearity response for the “sigmoidnet” network function.