A family of spatial SUR results when the subvectors of unknown
parameters vector q ¼ [g, b0 , l, S] are set to be zero. For example, if
the vector g ¼ 0, the model specifications become the spatial SUR
with spatially autocorrelated disturbance, while the model specifications
are the spatial SUR with spatially autocorrelated dependent
variables, if the vector l ¼ 0.