/usr/share/doc/ruby-gsl/examples/odeiv/ 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/odeiv/binarysystem.gp
/usr/share/doc/ruby-gsl/examples/odeiv/binarysystem.rb
/usr/share/doc/ruby-gsl/examples/odeiv/demo.gp
/usr/share/doc/ruby-gsl/examples/odeiv/demo.rb
/usr/share/doc/ruby-gsl/examples/odeiv/demo2.gp
/usr/share/doc/ruby-gsl/examples/odeiv/duffing.rb
/usr/share/doc/ruby-gsl/examples/odeiv/frei1.rb
/usr/share/doc/ruby-gsl/examples/odeiv/frei2.rb
/usr/share/doc/ruby-gsl/examples/odeiv/legendre.rb
/usr/share/doc/ruby-gsl/examples/odeiv/odeiv.rb
/usr/share/doc/ruby-gsl/examples/odeiv/odeiv2.rb
/usr/share/doc/ruby-gsl/examples/odeiv/oscillator.rb
/usr/share/doc/ruby-gsl/examples/odeiv/sedov.rb
/usr/share/doc/ruby-gsl/examples/odeiv/whitedwarf.gp
/usr/share/doc/ruby-gsl/examples/odeiv/whitedwarf.rb