“…3 For some recent references in the control literature, see, e.g., Braci & Diop (2001); Busvelle & Gauthier (2003); Chitour (2002); Dabroom & Khalil (1999); Diop, Fromion & Grizzle (2001); Diop, Grizzle & Chaplais (2000); Diop, Grizzle, Moraal & Stefanopoulou (1994) ;Duncan, Madl & Pasik-Duncan (1996); Ibrir (2003Ibrir ( , 2004; Ibrir & Diop (2004); Kelly, Ortega, Ailon & Loria (1994); Levant (1998Levant ( , 2003; Su, Zheng, Mueller & Duan (2006). The literature on numerical differentiation might be even larger in signal processing and in other fields of engineering and applied mathematics.…”