Pfaffian constraint

In dynamics, a Pfaffian constraint is a way to describe a dynamical system in the form:

${\displaystyle \sum _{s=1}^{n}A_{rs}du_{s}+A_{r}dt=0;\;r=1,\ldots ,L}$^[1]

where ${\displaystyle L}$ is the number of equations in a system of constraints.

Holonomic systems can always be written in Pfaffian constraint form.