  On the basis of the method of iterative summation of path integrals (ISPI),
we develop a numerically exact transfer-matrix method to describe the
nonequilibrium properties of interacting quantum-dot systems. For this, we map
the ISPI scheme to a transfer-matrix approach, which is more accessible to
physical interpretation, allows for a more transparent formulation of the
theory, and substantially improves the efficiency. In particular, the
stationary limit is directly implemented, without the need of extrapolation.
The resulting new method, referred to as "transfer-matrix summation of path
integrals" (TraSPI), is then applied to resonant electronic transport through a
single-level quantum dot.
