## Cauchy characteristic matching in numerical relativity

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- Written by Chris Stevens

An important aspect of a simulation in numerical relativity is the extraction of the emitted gravitational waves, which is non-trivial since the simulation is on a physical domain of finite extent but gravitational waves are unambiguously defined only at future null infinity. There are a number of methods for waveform estimation, but only in characteristic extraction is the waveform calculated at scri+.

We present a new algorithm and implementation of characteristic extraction. It has the key feature of being simply extendible to characteristic matching, in which the characteristic evolution provides outer boundary data for the "3+1" simulation. The key advantage of characteristic matching is that it would lead to a significant speed-up in the time required to complete a numerical simulation.