Phase-space divergence
= Phase-space divergence
{title2=$\nabla_z\cdot b$}
The <divergence> of the vector field generating a flow on <phase space>. Its time integral determines the <Jacobian determinant> of the <characteristic flow map>: $d\log|\det D\Phi_t|/dt=(\nabla_z\cdot b)(\Phi_t,t)$. A <Hamiltonian vector field> has zero phase-space divergence in <canonical coordinates>.