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Abstract

Astronomical observations place increasingly tighter and more diverse
constraints on the properties of neutron stars (NS). Examples include
observations of radio or gamma-ray pulsars, accreting neutron stars and x-ray
bursts, magnetar giant flares, and recently, the gravitational waves (GW) from
coalescing binary neutron stars. Computing NS properties for a given EOS, such
as mass, radius, moment of inertia, tidal deformability, and innermost stable
circular orbits (ISCO), is therefore an important task. This task is
unnecessarily difficult because relevant formulas are scattered throughout the
literature and publicly available software tools are far from being complete
and easy to use. Further, naive implementations are unreliable in numerical
corner cases, most notably when using equations of state (EOS) with phase
transitions. To improve the situation, we provide a public library for
computing NS properties and handling of EOS data. Further, we include a
collection of EOS based on existing nuclear physics models together with
precomputed sequences of NS models. All methods are accessible via a Python
interface. This article collects all relevant equations and numerical methods
in full detail, including a novel formulation for the tidal deformability
equations suitable for use with phase transitions. As a sidenote to the topic
of ISCOs, we discuss the stability of non-interacting dark matter particle
circular orbits inside NSs. Finally, we present some simple applications
relevant for parameter estimation studies of GW data. For example, we explore
the validity of universal relations, and discuss the appearance of multiple
stable branches for parametrized EOS.