/usr/share/doc/ruby-gsl/examples/poly/ 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/poly/bell.rb
/usr/share/doc/ruby-gsl/examples/poly/bessel.rb
/usr/share/doc/ruby-gsl/examples/poly/cheb.rb
/usr/share/doc/ruby-gsl/examples/poly/cheb_II.rb
/usr/share/doc/ruby-gsl/examples/poly/cubic.rb
/usr/share/doc/ruby-gsl/examples/poly/demo.rb
/usr/share/doc/ruby-gsl/examples/poly/eval.rb
/usr/share/doc/ruby-gsl/examples/poly/eval_derivs.rb
/usr/share/doc/ruby-gsl/examples/poly/fit.rb
/usr/share/doc/ruby-gsl/examples/poly/hermite.rb
/usr/share/doc/ruby-gsl/examples/poly/poly.rb
/usr/share/doc/ruby-gsl/examples/poly/quadratic.rb