  A self-consistent linear-response theory for a two-lead mesoscopic structure
in Landauer's viewpoint for transport is developed. A density operator relevant
in this viewpoint, in a uniform magnetic field is derived. It is shown that
this operator differs from the one given in Kubo's viewpoint by a term that
represents the self-consistent effects. Hence, a special emphasis is devoted to
the diagonal master equation where an exact solution is obtained in the
framework of elastic scattering theory.
