@misc{indiciae99b592e4e88f,
  title = {Computer program for solving ground-water flow equations by the preconditioned conjugate gradient method},
  author = {L.K. Kuiper},
  year = {1987},
  doi = {10.3133/wri874091},
  url = {https://pubs.usgs.gov/publication/wri874091},
  note = {Source identifier: wri874091}
}