The Lipschitz constant of a map between metric spaces
is the least
for which
for all
, when such a finite constant
exists. Equivalently, it is the supremum of the ratios
over distinct
.
For a domain with at most one point, the constant
is zero.
A map with Lipschitz constant at most one is nonexpansive. On the vector space of real Lipschitz functions vanishing at a fixed base point, the Lipschitz constant is a norm. This function space is used to define the Lipschitz-free space.