The Divergence of a Vector
Evaluate the divergence of the vector \mathbf{v}=v_{x} \mathbf{e}_{x}+v_{y} \mathbf{e}_{y}, which represents the velocity of a traveling wave (see Section 7.11), and whose components are:
v_{x}=-c e^{k y} \sin (k x-\omega t), \quad v_{y}=c e^{k y} \cos (k x-\omega t) . (E5.2.1)