@unpublished{RattanaBoeckmann2012,
  author  = {Amornrat Rattana and Christine B{\"o}ckmann},
  title   = {Matrix methods for computing Eigenvalues of Sturm-Liouville problems of order four},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprints des Instituts f{\"u}r Mathematik der Universit{\"a}t Potsdam},
  number    = {1(2012)13},
  year    = {2012},
}