The authors investigate the subject of linear dynamics by studying the notion of frequent hypercyclicity for bounded operators
on separable complex
is frequently hypercyclic if there exists a vector
such that for every nonempty open subset
, the set of integers
has positive lower density. They give several criteria for frequent hypercyclicity, and this leads them in particular to study linear transformations from the point of view of ergodic theory. Several other topics which are classical in hypercyclicity theory are also investigated in the frequent hypercyclicity setting.