This gives a single four - dimensional state vector for the radiative contributions from the forcing and feedbacks, given a particular forcing. (realclimate.org)
When two particles interact, they form a composite quantum system, described by a single state vector, even when one particle flies far away from the other. (sciencenews.org)
As Weinberg points out, a given set of state vectors will tell you what the density matrix is. (sciencenews.org)