  The Lindblad equation is an evolution equation for the density matrix in
quantum theory. It is the general linear, Markovian, form which ensures that
the density matrix is hermitian, trace 1, positive and completely positive.
Some elementary examples of the Lindblad equation are given. The derivation of
the Lindblad equation presented here is "simple" in that all it uses is the
expression of a hermitian matrix in terms of its orthonormal eigenvectors and
real eigenvalues. Thus, it is appropriate for students who have learned the
algebra of quantum theory. Where helpful, arguments are first given in a
two-dimensional hilbert space.
