@article{11185,
  author = {Bj{\o}rn Nielsen and Kent-Andre Mardal},
  title = {Efficient Preconditioners for Optimality Systems Arising in Connection With Inverse Problems},
  year = {2010},
  journal = {SIAM Journal on Control and Optimization},
  volume = {48},
  number = {8},
  doi = {10.1137/080719960},
}