“…Many different approaches to the problem exist including (i) Pohjanpalo's power series expansion (Pohjanpalo, 1978), (ii) application of Fliess' series expansion (Tunali & Tarn, 1987;Walter & Pronzato, 1996) (iii) application of non-linear control theory and, more specifically, non-linear observability (Hermann & Krener, 1977;Isidori, 1989;Kwatny & Blankenship, 2000), (iii) the similarity transformation approach (Denis-Vidal & Joly-Blanchard, 2004;Denis-Vidal, Joly-Blanchard, & Noiret, 2001;Tunali & Tarn, 1987), (iv) differential algebra methods (Anguelova, Karlsson, & Jirstrand, 2012;Denis-Vidal et al, 2001;Ljung & Glad, 1994;Saccomani, 2004;Saccomani, Audoly, & D'Angió, 2003;Sedoglavic, 2002), and (v) a sensitivity based analysis (Brun & Reichert, 2001;Quaiser & Mönnigmann, 2009). A summary of the various approaches can be found in a recent review paper by Miao and co-workers (Miao, Xia, Perelson, & Wu, 2011).…”