Divergence : divergence

divergence takes two arguments : a vector field of dimension n depending on n real variables.
divergence returns the divergence of F that is the sum of the derivative of the k-th component with respect to the k-th variable. For example in dimension n = 3:

divergence([A,B,C],[x,y,z])= $${\frac{{\partial A}}{{\partial x}}}$$ + $${\frac{{\partial B}}{{\partial y}}}$$ + $${\frac{{\partial C}}{{\partial z}}}$$

Input :

divergence([x*z,-y^2,2*x^y],[x,y,z])

Output :

z+-2*y