  Schubert varieties have been exhaustively studied with a plethora of
techniques: Coxeter groups, explicit desingularization, Frobenius splitting,
etc. Many authors have applied these techniques to various other varieties,
usually defined by determinantal equations. It has turned out that most of
these apparently different varieties are actually Schubert varieties in
disguise, so that one may use a single unified theory to understand many large
families of spaces.
  The most powerful result in this direction was given by Lusztig as a footnote
to his work on canonical bases. He showed that the variety of nilpotent
representations of a cyclic quiver (including nilpotent conjugacy classes of
matrices) is isomorphic to an open subset of a Schubert variety for the loop
group GL(n)^. In this paper, we attempt to describe the affine Schubert
varieties and Lusztig's isomorphism in the simplest terms possible.
  We then apply this isomorphism to an interesting example, the variety of
circular complexes, recovering some results of Mehta and Trivedi.
