Adding Llama to the ET

In order to add Llama to the ET, we require:

• Tests
• Documentation
• Example(s)

The Llama infrastructure has been used in many published papers, so is clearly considered robust enough to produce correct scientific results.

Tests

We have the following test cases:

• Llama/Coordinates/test/test7patch: Sets up the 7-patch system. Checks coordinates. Makes sure that this doesn't crash. No evolution.
• Llama/LlamaWaveToy/test/llamawavetoy_6patch.par: Sets up 6-patch (spherical) system. Evolves l=2,m=2 x Gaussian for 4 iterations. Checks 1D ASCII output. Runs on any number of processes (only 1 and 2 have been tested).
• Llama/LlamaWaveToy/test/llamawavetoy_7patch.par: Same as 6-patch but uses 7-patch system. Works on 1 process. Currently has a problem on 2 processes; looks like a bug. Assertion failure from Carpet. Restricted to run on 1 process as a result.
• McLachlan/ML_BSSN_Test/test/ML_BSSN_MP_O8_bh.par: Runs a few iterations of BBH initial data using 8th order McLachlan on 7-patch (spherical+Cartesian) system. Currently fails on my laptop with tolerance errors.

Documentation

The following thorns have documentation:

• Coordinates: Provides an introduction to the Llama multipatch infrastructure and the different patch systems
• GlobalDerivative: Describes the multipatch-aware finite differencing implementation
• Interpolate2: Interpatch interpolation
• LlamaWaveToy: A scalar wave equation on various backgrounds.
• WaveExtractL: Llama-optimised wave extraction using Zerilli-Moncrief and Regge-Wheeler gauge invariant perturbations of Schwarzschild

The documentation is probably not all up-to-date; there are comments in some of the files that the description does not match what is implemented.

Examples

There are three examples in LlamaWaveToy/par:

• Kerr-Schild_Gaussian.par: Radial Gaussian evolved with wave equation on Kerr-Schild background. Uses 6-patch (spherical) system.
• Kerr-Schild_Multipole.par: l=2, m=2 mode with radial Gaussian evolved on a Kerr-Schild background. Uses 6-patch (spherical) system.
• Minkowski_Multipole.par: l=2, m=2 mode with radial Gaussian evolved on a flat background. Uses 7-patch (spherical+Cartesian) system.

These run in about 20 minutes on a laptop, and evolve a wave on a given background. These have been tested and work.

There is a new Multipatch Wave Equation gallery page based on the Kerr-Schild_Multipole example (not yet linked to the main gallery page).

There is also the GW150914 gallery page.