C. Bernardi et al., INTERPOLATION OF NULLSPACES OF DIFFERENTI AL-OPERATORS WITH APPLICATION TO SPECTRAL METHODS, Comptes rendus de l'Academie des sciences. Serie 1, Mathematique, 318(4), 1994, pp. 373-378
We present some results concerning the interpolation of nullspaces of
the same differential operator in Sobolev spaces of different orders,
with or without boundary conditions. As an application, we derive the
optimal approximation of divergence-free functions by high degree dive
rgence-free polynomials.