TY  - RPRT
TI  - Preconditioned Conjugate-Gradient 2 (PCG2), a computer program for solving ground-water flow equations
AU  - Mary C. Hill
PY  - 1990
DO  - 10.3133/wri904048
UR  - https://pubs.usgs.gov/publication/wri904048
ID  - wri904048
ER  -