We consider, as an example, a
parametric family of periodic boundary value problems for the diffusion
equation with the diffusion coefficient equal to a small constant in a
subdomain. Such problems typically appear in the process of
homogenization of composites with a periodic structure.
They are not uniformly well-posed when the constant gets
small. However, we suggest a natural implicit splitting of the problem into two well-posed problems. Using this
idea, we prove a uniform convergence of a standard preconditioned
iterative method with a special initial guess. In all our arguments
we use a natural parameter-independent Sobolev norm, not the energy norm.
We also discuss FEM error estimates for such problems, and
mention some results for the
mixed formulation of the problem.
Schlumberger-Doll Research,
Ridgefield, CT, January 26, 1998