  We present a numerical method to compute the Landauer conductance of
noninteracting two-dimensional massless Dirac fermions in disordered systems.
The method allows for the introduction of boundary conditions at the ribbon
edges and accounts for an external magnetic field. By construction, the
proposed discretization scheme avoids the fermion doubling problem. The method
does not rely on an atomistic basis and is particularly useful to deal with
long-range disorder, the correlation length of which largely exceeds the
underlying material crystal lattice spacing. As an application, we study the
case of monolayer graphene sheets with zigzag edges subjected to long-range
disorder, which can be modeled by a single-cone Dirac equation.
