I read paper about Horn-Schunck multiscale method for computing optical flow
Core part of this algorithm is minimizing some functional. One part of functional contains nonlinear term inside L2 norm. Author uses Taylor expansion to obtain linear approximation of term \begin{equation} I(x+h^{n+1}(x)) = I(x+h^n(x)) + \nabla I(x + h^n(x))(h^{n+1}(x) - h^n(x))\\ \end{equation} Then author takes first derivative of functional and obtains $h^{n+1}$ by solving linear equality. Then old $h^n$ are replaced by $h^{n+1}$ and we repeat calculation until convergence.
So my question is what name of this method?
PS Sorry for my poor English and math skills