  In numerous applications the mathematical model consists of different
processes coupled across a lower dimensional manifold. Due to the multiscale
coupling, finite element discretization of such models presents a challenge.
Assuming that only singlescale finite element forms can be assembled we present
here a simple algorithm for representing multiscale models as linear operators
suitable for Krylov methods. Flexibility of the approach is demonstrated by
numerical examples with coupling across dimensionality gap 1 and 2.
Preconditioners for several of the problems are discussed.

Numerical Analysis;Mathematical Software;Numerical Analysis