https://doi.org/10.1140/epja/s10050-026-01845-0
Code Paper
A modern Fortran library for 
coupling and recoupling coefficients
1
Department of Physics and Astronomy, University of Notre Dame, 46556-5670, Notre Dame, IN, USA
2
TRIUMF, V6T 2A3, Vancouver, BC, Canada
3
Physics Division, Argonne National Laboratory, 60439-4801, Argonne, IL, USA
4
Institute for Nuclear Theory, University of Washington, 98195-1550, Seattle, WA, USA
5
NextSilicon Inc., 55402-1572, Minneapolis, MN, USA
a
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Received:
14
August
2025
Accepted:
23
March
2026
Published online:
14
May
2026
Abstract
The group has applications in several branches of physics. Many of these applications depend on availability of coupling and recoupling coefficients. We have developed a modern Fortran library for calculation of the coupling coefficients, for both the 
and 
group chains, and the recoupling coefficients. The library implements the algorithms of Draayer, Akiyama, and Millener, which are laid out in the paper. Performance of the library has been tested and compared to the Akiyama-Draayer (AD) library implementing the same algorithms as well as to a more recent implementation. Our library works for a larger range of quantum numbers and provides more accurate coupling coefficients with large quantum numbers than the AD library.
Copyright comment Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
Communicated by Denis Lacroix.
Present address: NextSilicon Inc., Minneapolis, MN, 55402-1572, USA
© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
