@article{etna_vol26_pp209-227,
  author  = {Michele Benzi and Bora U\c{c}ar},
  title   = {Block triangular preconditioners for $M$-matrices and Markov chains},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {26},
  year    = {2007},
  pages   = {209--227},
}