A filtering technique for the temporally reduced matrix of the Wilson   fermion determinant
  The Wilson fermion determinant can be written in the form of a series expansion in fugacity $\xi=\exp(\mu/T)$, provided that the eigenmodes of the temporally reduced operator are obtained. Since the calculation of all eigenmodes rapidly becomes prohibitive for larger volumes, we develop a method to calculate only the low-energy eigenmodes of the reduced matrix using a matrix filetering technique. This provides a basis for an approximation to neglect uninteresting ultraviolet contributions. 
Yasunori Futamura, Shoji Hashimoto, Akira Imakura, Keitaro Nagata,   Tetsuya Sakurai
hep-lat