libnlopt-cxx-dev 2.6.1-8ubuntu2 (armhf binary) in ubuntu focal

 NLopt is a free/open-source library for nonlinear optimization, providing
 a common interface for a number of different free optimization routines
 available online as well as original implementations of various other
 algorithms. Its features include:
 .
    * Callable from C, C++, Fortran, GNU Octave, Python, GNU Guile, GNU R.
    * A common interface for many different algorithms
    * Support for large-scale optimization.
    * Both global and local optimization algorithms.
    * Algorithms using function values only (derivative-free) and also
      algorithms exploiting user-supplied gradients.
    * Algorithms for unconstrained optimization, bound-constrained optimization,
      and general nonlinear inequality/equality constraints.
 .
 This package contains the header files, static libraries and symbolic
 links that developers using NLopt library with C++ will need.