Max Wardetzky Miklós Bergou David Harmon Denis Zorin Eitan Grinspun Discrete quadratic curvature energies. 499-518 2007 24 Computer Aided Geometric Design 8-9 http://dx.doi.org/10.1016/j.cagd.2007.07.006 db/journals/cagd/cagd24.html#WardetzkyBHZG07