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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