Preprint of the project: DFG research group "Spectral analysis, asymptotic distributions and stochastic dynamics"Numerical approximation and spectral analysis of infinitedimensional dynamical systems03059 WolfJürgen Beyn, Thorsten Hüls. In this paper we consider heteroclinic orbits in discrete time dynamical systems that connect a hyperbolic fixed point to a nonhyperbolic fixed point with a onedimensional center direction. A numerical method for approximating the heteroclinic orbit by a finite orbit sequence is introduced and a detailed error analysis is presented. The loss of hyperbolicity requires special tools for proving the error estimate  the polynomial dichotomy of linear difference equations and a (partial) normal form transformation near the nonhyperbolic fixed point. This situation appears, for example, when one fixed point undergoes a flip bifurcation. For this case, the approximation method and the validity of the error estimate is illustrated by an example.
