/usr/share/doc/ruby-gsl/examples/gallery/butterfly.rb is in ruby-gsl 2.1.0.3+dfsg1-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | #!/usr/bin/env ruby
require("gsl")
phi = GSL::Vector.linspace(0, 12*Math::PI, 800)
r = GSL::Sf::exp(GSL::Sf::cos(phi)) - 2*GSL::Sf::cos(4*phi) + GSL::pow_5(GSL::Sf::sin(phi/12))
x = r*GSL::Sf::cos(phi)
y = r*GSL::Sf::sin(phi)
GSL::graph(x, y)
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