Gout = ResponseFunction.ReducePoles(Gin, NPoles) or Gout = ResponseFunction.ReducePoles(Gin, NPolesVal, NPolesCon) reduces the number of poles in $G_{in}$ to $N_{Poles}$ or to $N_{Poles}^{Val} + N_{Poles}^{Con}$ by merging poles close to each other with small spectral weight (residue) (see appendix of |Phys. Rev. B 90, 085102 for additional information). The algorithm with $N_{Poles}^{Val}$ and $N_{Poles}^{Con}$ set does not shift spectral weight between the conduction and valence states (set by the chemical potential).