  We test the Anderson prescription [1], a BCS formalism for describing
superconductivity in inhomogeneous systems, and compare results with those
obtained from the Bogoliubov-de Gennes formalism, using the attractive Hubbard
model with surfaces and nonmagnetic impurities. The Anderson approach captures
the essential features of the spatial variation of the gap parameter and
electron density around a surface or an impurity over a wide range of
parameters. It breaks down, however, in the strong-coupling regime for a weak
impurity potential.
  [1] P. W. Anderson, J. Phys. Chem. Solids 11, 26 (1959).
