/usr/share/doc/ruby-gsl/examples/linalg/ is in ruby-gsl 2.1.0.3+dfsg1-1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/doc/ruby-gsl/examples/linalg/HH.rb
/usr/share/doc/ruby-gsl/examples/linalg/HH_narray.rb
/usr/share/doc/ruby-gsl/examples/linalg/LQ_solve.rb
/usr/share/doc/ruby-gsl/examples/linalg/LU.rb
/usr/share/doc/ruby-gsl/examples/linalg/LU2.rb
/usr/share/doc/ruby-gsl/examples/linalg/LU_narray.rb
/usr/share/doc/ruby-gsl/examples/linalg/PTLQ.rb
/usr/share/doc/ruby-gsl/examples/linalg/QR.rb
/usr/share/doc/ruby-gsl/examples/linalg/QRPT.rb
/usr/share/doc/ruby-gsl/examples/linalg/QR_solve.rb
/usr/share/doc/ruby-gsl/examples/linalg/QR_solve_narray.rb
/usr/share/doc/ruby-gsl/examples/linalg/SV.rb
/usr/share/doc/ruby-gsl/examples/linalg/SV_narray.rb
/usr/share/doc/ruby-gsl/examples/linalg/SV_solve.rb
/usr/share/doc/ruby-gsl/examples/linalg/chol.rb
/usr/share/doc/ruby-gsl/examples/linalg/chol_narray.rb
/usr/share/doc/ruby-gsl/examples/linalg/complex.rb
/usr/share/doc/ruby-gsl/examples/linalg/invert_narray.rb