@article{Grytczuk:2009,
  author  = "A. Grytczuk and I. Kurzydło",
  title   = "On the matrix negative pell equation",
  journal = "Discussiones Mathematicae : General Algebra and Applications",
  volume  = "Vol. 29",
  number  = "no 1",
  pages   = "35--45",
  year    = "2009",
}