relates a vector of [[independent variables]], :<math>\mathbf{x}</math>, and its associated observed [[dependent variables]], '''<math>\mathbf{y'''}</math>. The function ''<math>f''</math> is nonlinear in the components of the vector of parameters ''β''<math>\beta</math>, but otherwise arbitrary. For example, the [[Michaelis–Menten]] model for enzyme kinetics has two parameters and one independent variable, related by ''<math>f''</math> by:{{efn|This model can also be expressed in the conventional biological notation:
:<math> v = \frac{V_\max\ [\mbox{S}]}{K_m + [\mbox{S}]} </math>
