  We consider a quantum quench of the trap frequency in a system of bosons
interacting through an inverse-square potential and confined in a harmonic trap
(the harmonic Calogero model). We determine exactly the initial state in terms
of the post-quench eigenstates and derive the time evolution of simple physical
observables. Since this model possesses an infinite set of integrals of motion
(IoM) that allow its exact solution, a generalised Gibbs ensemble (GGE), i.e. a
statistical ensemble that takes into account the conservation of all IoM, can
be proposed in order to describe the values of local physical observables long
after the quench. Even though, due to the presence of the trap, physical
observables do not exhibit equilibration but periodic evolution, such a GGE may
still describe correctly their time averaged values. We check this analytically
for the local boson density and find that the GGE conjecture is indeed valid,
in the thermodynamic limit.
