/usr/include/ql/experimental/math/ is in libquantlib0-dev 1.9.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/experimental/math/all.hpp
/usr/include/ql/experimental/math/claytoncopularng.hpp
/usr/include/ql/experimental/math/convolvedstudentt.hpp
/usr/include/ql/experimental/math/expm.hpp
/usr/include/ql/experimental/math/farliegumbelmorgensterncopularng.hpp
/usr/include/ql/experimental/math/fireflyalgorithm.hpp
/usr/include/ql/experimental/math/frankcopularng.hpp
/usr/include/ql/experimental/math/gaussiancopulapolicy.hpp
/usr/include/ql/experimental/math/hybridsimulatedannealing.hpp
/usr/include/ql/experimental/math/hybridsimulatedannealingfunctors.hpp
/usr/include/ql/experimental/math/isotropicrandomwalk.hpp
/usr/include/ql/experimental/math/laplaceinterpolation.hpp
/usr/include/ql/experimental/math/latentmodel.hpp
/usr/include/ql/experimental/math/levyflightdistribution.hpp
/usr/include/ql/experimental/math/moorepenroseinverse.hpp
/usr/include/ql/experimental/math/multidimintegrator.hpp
/usr/include/ql/experimental/math/multidimquadrature.hpp
/usr/include/ql/experimental/math/numericaldifferentiation.hpp
/usr/include/ql/experimental/math/particleswarmoptimization.hpp
/usr/include/ql/experimental/math/piecewisefunction.hpp
/usr/include/ql/experimental/math/piecewiseintegral.hpp
/usr/include/ql/experimental/math/polarstudenttrng.hpp
/usr/include/ql/experimental/math/tcopulapolicy.hpp
/usr/include/ql/experimental/math/zigguratrng.hpp