  We introduce a complex purity density and its associated current for pure
states of continuous variable systems. The scheme is constructed by analogy
with the notions of probability density and probability current. Taking
advantage of the formal continuity equations obtained this way we can introduce
an entanglement subdynamics. We suggest the use of the dimensionality of this
subdynamics as a potential measure of the complexity of entanglement. The
scheme also provides insights into the relation between the global and local
aspects of quantum correlations.
