  Numerical tools, such as OpenLoops, provide NLO scattering amplitudes for a
very wide range of hard scattering amplitudes in a fully automated way. In
order to match the numerical precision of current and future experiments,
however, the higher precision of NNLO calculations is essential, and their
automation in a similar tool highly desirable. In our approach, D-dimensional
amplitudes are decomposed into loop-momentum tensor integrals with coefficients
constructed in four dimensions and rational terms. We present a fully generic
algorithm for the efficient numerical construction of the tensor coefficients,
which constitutes an important building block for an automated NNLO tool.
