Dear all,

I would like to propose the inclusion of FLRWSolver in the Einstein Toolkit.

FLRWSolver is a thorn for cosmological initial conditions. It provides initial data for a flat, matter-dominated (dust), Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime with small (linear) perturbations. Both simplified “toy” initial data and realistic perturbations are currently supported. The latter consists of Gaussian-random fluctuations to the background drawn from a user-provided matter power spectrum. The user therefore only needs to provide the power spectrum of density fluctuations and specify the FLRW background characteristics to perform a realistic cosmological simulation of nonlinear structure formation using the ET. Numerical relativity has proven an extremely useful tool to study general relativistic effects in nonlinear cosmology, and the ET + FLRWSolver provides a useful framework for such studies (see, e.g. https://arxiv.org/abs/1807.01711 https://arxiv.org/abs/1807.01711).

FLRWSolver has been used in several publications, and has been public for ~2 years at this repository: https://github.com/hayleyjm/FLRWSolver_public https://github.com/hayleyjm/FLRWSolver_public, and already has 4-6 users (as far as I know).

If you are already using FLRWSolver, may be interested in using it in the future, or are just interested in seeing it as a part of the ET, please comment on this enhancement ticket: https://bitbucket.org/einsteintoolkit/tickets/issues/2549/inlcude-flrwsolver... https://bitbucket.org/einsteintoolkit/tickets/issues/2549/inlcude-flrwsolver-in-et

I am working towards including FLRWSolver in the next release, but if there are any feedback/suggestions in the meantime then please don’t hesitate to reply/contact me. I’m more than happy to improve/extend FLRWSolver (and even delay to the following release if need be) if it’s in the best interest of the community.

Best wishes, Hayley

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Hayley Macpherson

Email: hayleyjmacpherson@gmail.com Pronouns: she/her/hers

Office: my house (usually B1.23) Centre for Theoretical Cosmology DAMTP, University of Cambridge Wilberforce Road CB3 0WA Cambridge United Kingdom