@article{etna_vol58_pp394-401,
  author  = {William Layton and Shuxian Xu},
  title   = {Conditioning of linear systems arising from penalty methods},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {58},
  year    = {2023},
  pages   = {394--401},
  doi     = {10.1553/etna_vol58s394},
}