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:…message-passing (Wainwright et al., 2005b)
• Fractional belief propagation (Wiegerinck & Heskes, 2002)
• Power EP (Minka, 2004)
One way to understand these algorithms is to view their cost functions as free-energy functions from statistical physics (Yedidia et al., 2004; Heskes, 2003).
Category: