/usr/share/doc/ruby-gsl/examples/fit/ 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/fit/expfit.rb
/usr/share/doc/ruby-gsl/examples/fit/gaussfit.rb
/usr/share/doc/ruby-gsl/examples/fit/gaussian_2peaks.rb
/usr/share/doc/ruby-gsl/examples/fit/hillfit.rb
/usr/share/doc/ruby-gsl/examples/fit/lognormal.rb
/usr/share/doc/ruby-gsl/examples/fit/lorentzfit.rb
/usr/share/doc/ruby-gsl/examples/fit/multifit.rb
/usr/share/doc/ruby-gsl/examples/fit/ndlinear.rb
/usr/share/doc/ruby-gsl/examples/fit/nonlinearfit.rb
/usr/share/doc/ruby-gsl/examples/fit/plot.gp
/usr/share/doc/ruby-gsl/examples/fit/polyfit.rb
/usr/share/doc/ruby-gsl/examples/fit/powerfit.rb
/usr/share/doc/ruby-gsl/examples/fit/sigmoidfit.rb
/usr/share/doc/ruby-gsl/examples/fit/sinfit.rb
/usr/share/doc/ruby-gsl/examples/fit/wlinear.rb