@article{etna_vol59_pp270-294,
  author  = {J. Chen and V. Dwarka and C. Vuik},
  title   = {A matrix-free parallel solution method for the three-dimensional heterogeneous Helmholtz equation},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {59},
  year    = {2023},
  pages   = {270--294},
  doi     = {10.1553/etna_vol59s270},
}