Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:which is exactly the cost function that leads to the nonlinear LPM-ICA algorithm (or particularly the LPM-ICA algorithm at the special case f ðrÞ 1⁄4 r) (Xu, Yang, & Amari, 1996; Xu, 1998b; Xu et al., 1998).
Category: