@article{etna_vol29_pp70-80,
  author  = {Matthias Bolten},
  title   = {Hierarchical grid coarsening for the solution of the Poisson equation in free space},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {29},
  year    = {2007-2008},
  pages   = {70--80},
}