The infinitesimal generator of a strongly continuous semigroup on a Banach space
is the linear operator
defined by
for every
for which the limit exists. These vectors form the domain of
. The infinitesimal generator is a densely defined closed
operator and uniquely determines the semigroup. For a contraction
semigroup, the Lumer-Phillips theorem
characterizes the infinitesimal generator as an
-dissipative operator.