Semisymplectic group and Hamiltonian vector fields

The purpose of this paper is presenting a theoretical basis for the study of $\omega$-Hamiltonian vector fields in a more general approach than the classical one. We introduce the concepts of $\omega$-symplectic group and $\omega$-semisymplectic group, and describe some of their properties. We show that the Lie algebra of such groups is a useful tool in the recognition of an $\omega$-Hamiltonian vector field defined on a symplectic vector space $(V,\omega)$ with respect to coordinates that are not necessarily symplectic.