@misc{indiciae64882ee73022,
  title = {Preconditioned Conjugate-Gradient 2 (PCG2), a computer program for solving ground-water flow equations},
  author = {Mary C. Hill},
  year = {1990},
  doi = {10.3133/wri904048},
  url = {https://pubs.usgs.gov/publication/wri904048},
  note = {Source identifier: wri904048}
}