Function File: [y, J] = D (F, x, varargin)

Evaluate F for a given input x and compute the jacobian, such that

          
                     d
          J(i,j) = ----- y(i) where y = F(x, varargin{:})
                   dx(j)
          

If x is complex, the above holds for the directional derivatives along the real axis

Derivatives are computed analytically via Automatic Differentiation