/usr/include/ql/methods/finitedifferences/ is in libquantlib0-dev 1.1-2build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/methods/finitedifferences/all.hpp
/usr/include/ql/methods/finitedifferences/americancondition.hpp
/usr/include/ql/methods/finitedifferences/boundarycondition.hpp
/usr/include/ql/methods/finitedifferences/bsmoperator.hpp
/usr/include/ql/methods/finitedifferences/bsmtermoperator.hpp
/usr/include/ql/methods/finitedifferences/cranknicolson.hpp
/usr/include/ql/methods/finitedifferences/dminus.hpp
/usr/include/ql/methods/finitedifferences/dplus.hpp
/usr/include/ql/methods/finitedifferences/dplusdminus.hpp
/usr/include/ql/methods/finitedifferences/dzero.hpp
/usr/include/ql/methods/finitedifferences/expliciteuler.hpp
/usr/include/ql/methods/finitedifferences/fdtypedefs.hpp
/usr/include/ql/methods/finitedifferences/finitedifferencemodel.hpp
/usr/include/ql/methods/finitedifferences/impliciteuler.hpp
/usr/include/ql/methods/finitedifferences/mixedscheme.hpp
/usr/include/ql/methods/finitedifferences/onefactoroperator.hpp
/usr/include/ql/methods/finitedifferences/operatorfactory.hpp
/usr/include/ql/methods/finitedifferences/operatortraits.hpp
/usr/include/ql/methods/finitedifferences/parallelevolver.hpp
/usr/include/ql/methods/finitedifferences/pde.hpp
/usr/include/ql/methods/finitedifferences/pdebsm.hpp
/usr/include/ql/methods/finitedifferences/pdeshortrate.hpp
/usr/include/ql/methods/finitedifferences/shoutcondition.hpp
/usr/include/ql/methods/finitedifferences/stepcondition.hpp
/usr/include/ql/methods/finitedifferences/tridiagonaloperator.hpp
/usr/include/ql/methods/finitedifferences/zerocondition.hpp