[Users] FUKAv2 Release

[Samuel Tootle]

Dear ETK community members,

The following is a notification of the release of the second version of the Frankfurt/Kadath (FUKA) initial data (ID) codes.

FUKA is a collection of publicly available initial data codes to provide access to highly asymmetric, spinning compact object binaries such as binary black holes, binary neutron stars, and black hole-neutron star binaries. FUKA was originally released June, 2021 (https://hyperspace.uni-frankfurt.de/2021/06/25/fuka-frankfurt-uni-kadath-initial-data-solvers/), however, development has continued in order to enable the reliable generation of initial data for extremal configurations (i.e., highly asymmetric binaries with different near extremal spins) while providing an intuitive interface to the user and minimizing the workflow to obtain such ID.

To this end, FUKAv2 is a complete rewrite of the solver codes to enable each binary solver to utilize super-imposed isolated compact object solutions to generate the initial setup. This provides a stable setup for each binary solver to obtain a converged solution with only minimal effort on the frontend by the user.

Additionally, the solvers are now capable of automating the regridding procedure to obtain the desired final resolution while minimizing computation costs.

Finally, the key features available within the original FUKAv1 codes have also been integrated into v2 allowing one to easily obtain eccentricity reduced initial data either by using the built-in 3.5th order post-Newtonian estimates or by providing eccentricity reduction parameters manually (e.g., those obtained from iterative eccentricity reduction).

Overall, when comparing to the original v1 codes FUKAv2 is more than 5x more efficient when solving the ID for asymmetric spinning binaries with a vastly more robust framework to maximize convergence. Even more so, the effort on the user has been significantly reduced by removing the need to manually create setups, solve, then regrind.

The latest version of FUKA along with the thorns enabling the import of FUKA ID into the Einstein Toolkit are available at: https://bitbucket.org/fukaws/

As a final note, I will discuss some of these details during my lightning talk at the ETK Workshop next week which is currently scheduled for Tuesday, 11:50am PST.

Warm regards,
Samuel Tootle
PhD Candidate
Goethe Universität Frankfurt
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