A symmetric hyperbolic formulation of the vacuum Einstein equations in affine-null coordinates

We present a symmetric hyperbolic formulation of the Einstein equations in affine-null coordinates. Giannakopoulos et al. [Phys. Rev. D 102, 064035 (2020)] recently showed that most commonly numerically implemented formulations coordinates (and other single-null coordinate systems) are only weakly—not strongly—hyperbolic. By making use tetrad-based Newman–Penrose formalism, our avoids hyperbolicity problems investigated by (2020)]. discuss potential application for studying gravitational wave scattering.