  The aim of this paper is to prove that a control affine system on a manifold
is equivalent by diffeomorphism to a linear system on a Lie group or a
homogeneous space if and only the vector fields of the system are complete and
generate a finite dimensional Lie algebra. A vector field on a connected Lie
group is linear if its flow is a one parameter group of automorphisms. An
affine vector field is obtained by adding a left invariant one. Its projection
on a homogeneous space, whenever it exists, is still called affine. Affine
vector fields on homogeneous spaces can be characterized by their Lie brackets
with the projections of right invariant vector fields. A linear system on a
homogeneous space is a system whose drift part is affine and whose controlled
part is invariant. The main result is based on a general theorem on finite
dimensional algebras generated by complete vector fields, closely related to a
theorem of Palais, and which have its own interest. The present proof makes use
of geometric control theory arguments.
