  This paper presents alpaqa, an open-source C++ implementation of an augmented
Lagrangian method for nonconvex constrained numerical optimization, using the
first-order PANOC algorithm as inner solver. The implementation is packaged as
an easy-to-use library that can be used in C++ and Python. Furthermore, two
improvements to the PANOC algorithm are proposed and their effectiveness is
demonstrated in NMPC applications and on the CUTEst benchmarks for numerical
optimization. The source code of the alpaqa library is available at
https://github.com/kul-optec/alpaqa and binary packages can be installed from
https://pypi.org/project/alpaqa .
