/usr/share/doc/ruby-gsl/examples/matrix/ 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/matrix/a.dat
/usr/share/doc/ruby-gsl/examples/matrix/add.rb
/usr/share/doc/ruby-gsl/examples/matrix/b.dat
/usr/share/doc/ruby-gsl/examples/matrix/cat.rb
/usr/share/doc/ruby-gsl/examples/matrix/colvectors.rb
/usr/share/doc/ruby-gsl/examples/matrix/complex.rb
/usr/share/doc/ruby-gsl/examples/matrix/det.rb
/usr/share/doc/ruby-gsl/examples/matrix/diagonal.rb
/usr/share/doc/ruby-gsl/examples/matrix/get_all.rb
/usr/share/doc/ruby-gsl/examples/matrix/hilbert.rb
/usr/share/doc/ruby-gsl/examples/matrix/iterator.rb
/usr/share/doc/ruby-gsl/examples/matrix/matrix.rb
/usr/share/doc/ruby-gsl/examples/matrix/minmax.rb
/usr/share/doc/ruby-gsl/examples/matrix/mul.rb
/usr/share/doc/ruby-gsl/examples/matrix/rand.rb
/usr/share/doc/ruby-gsl/examples/matrix/read.rb
/usr/share/doc/ruby-gsl/examples/matrix/rowcol.rb
/usr/share/doc/ruby-gsl/examples/matrix/set.rb
/usr/share/doc/ruby-gsl/examples/matrix/set_all.rb
/usr/share/doc/ruby-gsl/examples/matrix/view.rb
/usr/share/doc/ruby-gsl/examples/matrix/view_all.rb
/usr/share/doc/ruby-gsl/examples/matrix/write.rb