@article{etna_vol40_pp414-435,
  author  = {Thomas Mach and Miroslav S. Prani\'c and Raf Vandebril},
  title   = {Computing approximate extended Krylov subspaces without explicit inversion},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {40},
  year    = {2013},
  pages   = {414--435},
}