Defining functions specify a curve of a particular type. They are used by the continuer to compute a point of a curve. The total number of the defining functions is one less than the size of a point (including active parameters, i.e. the parameters that may vary).

Usually, defining functions consist of equations specifying a phase object (for example, an equilibrium or a cycle) and equations defining its singularity (for example, the presence of eigenvalues on the imaginary axis or on the unit circle). They are constructed by MatCont automatically, based on the type of the dynamical system and the computed curve.