@ARTICLE{FrRuWi11,
  author = {Franken, Martina and Rumpf, Martin and Wirth, Benedikt},
  title = {A Phase Field based {PDE} Constraint Optimization Approach to Time
	Discrete {W}illmore Flow},
  journal = {International Journal of Numerical Analysis and Modeling},
  year = {2013},
  volume = {10},
  pages = {116--138},
  number = {1},
  pdf = {http://numod.ins.uni-bonn.de/research/papers/public/FrRuWi11.pdf},
}