potential takes two arguments : a vector field
V in R^{n} with respect to n real variables
and the vector of these variable names.

potential returns, if it is possible, a function U such that
grad(U)=V. When it is possible, we
say that V derives the potential U, and
U is defined up to a constant.

potential is the reciprocal function of derive.

Input :

potential([2*x*y+3,x

`^`

2-4*z,-4*y],[x,y,z])Output :

2*y*x

`^`

2/
2+3*x+(x`^`

2-4*z-2*x`^`

2/2)*y
Note that in ℝ^{3}
a vector V is a gradient if and only if its
rotational is zero i.e. if curl(V)=0.
In time-independent electro-magnetism,
V=E is the
electric field and U is the electric potential.