A method based on the Rayleigh-Ritz or Galerkin technique is presented for obtaining domains of linear stability in terms of the parameter space for space-dependent reactor dynamics models. The method developed is computationally economical because previous calculations are retained as the order of approximation increases. In addition, the method reduces to finding the eigenvalues of a matrix so any standard procedure can be used.,The method is applied to data typical of a fast and a thermal reactor with fuel and coolant feedback. One group of delayed neutrons is also included.