  Versal deformation of a matrix A is a normal form to which all matrices A +
E, close to A, can be reduced by similarity transformation smoothly depending
on the entries of A + E. In this paper we discuss versal deformations and their
use in codimension computations, in investigation of closure relations of
orbits and bundles, in studying changes of canonical forms under perturbations,
as well as in reduction of unstructured perturbations to structured
perturbations.
