/usr/include/dlib/matrix/ is in libdlib-dev 18.18-1.
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/usr/include/dlib/matrix/cblas_constants.h
/usr/include/dlib/matrix/lapack/
/usr/include/dlib/matrix/lapack/fortran_id.h
/usr/include/dlib/matrix/lapack/gees.h
/usr/include/dlib/matrix/lapack/geev.h
/usr/include/dlib/matrix/lapack/geqrf.h
/usr/include/dlib/matrix/lapack/gesdd.h
/usr/include/dlib/matrix/lapack/gesvd.h
/usr/include/dlib/matrix/lapack/getrf.h
/usr/include/dlib/matrix/lapack/ormqr.h
/usr/include/dlib/matrix/lapack/potrf.h
/usr/include/dlib/matrix/lapack/syev.h
/usr/include/dlib/matrix/lapack/syevr.h
/usr/include/dlib/matrix/matrix.h
/usr/include/dlib/matrix/matrix_abstract.h
/usr/include/dlib/matrix/matrix_assign.h
/usr/include/dlib/matrix/matrix_assign_fwd.h
/usr/include/dlib/matrix/matrix_blas_bindings.h
/usr/include/dlib/matrix/matrix_cholesky.h
/usr/include/dlib/matrix/matrix_conj_trans.h
/usr/include/dlib/matrix/matrix_conv.h
/usr/include/dlib/matrix/matrix_conv_abstract.h
/usr/include/dlib/matrix/matrix_data_layout.h
/usr/include/dlib/matrix/matrix_data_layout_abstract.h
/usr/include/dlib/matrix/matrix_default_mul.h
/usr/include/dlib/matrix/matrix_eigenvalue.h
/usr/include/dlib/matrix/matrix_exp.h
/usr/include/dlib/matrix/matrix_exp_abstract.h
/usr/include/dlib/matrix/matrix_expressions.h
/usr/include/dlib/matrix/matrix_fft.h
/usr/include/dlib/matrix/matrix_fft_abstract.h
/usr/include/dlib/matrix/matrix_fwd.h
/usr/include/dlib/matrix/matrix_generic_image.h
/usr/include/dlib/matrix/matrix_la.h
/usr/include/dlib/matrix/matrix_la_abstract.h
/usr/include/dlib/matrix/matrix_lu.h
/usr/include/dlib/matrix/matrix_mat.h
/usr/include/dlib/matrix/matrix_mat_abstract.h
/usr/include/dlib/matrix/matrix_math_functions.h
/usr/include/dlib/matrix/matrix_math_functions_abstract.h
/usr/include/dlib/matrix/matrix_op.h
/usr/include/dlib/matrix/matrix_qr.h
/usr/include/dlib/matrix/matrix_read_from_istream.h
/usr/include/dlib/matrix/matrix_subexp.h
/usr/include/dlib/matrix/matrix_subexp_abstract.h
/usr/include/dlib/matrix/matrix_trsm.h
/usr/include/dlib/matrix/matrix_utilities.h
/usr/include/dlib/matrix/matrix_utilities_abstract.h
/usr/include/dlib/matrix/symmetric_matrix_cache.h
/usr/include/dlib/matrix/symmetric_matrix_cache_abstract.h