/usr/ is in ruby-lapack 1.8.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/numru/
/usr/lib/ruby/vendor_ruby/numru/lapack.rb
/usr/lib/x86_64-linux-gnu/
/usr/lib/x86_64-linux-gnu/ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.5.0/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.5.0/numru/
/usr/lib/x86_64-linux-gnu/ruby/vendor_ruby/2.5.0/numru/lapack.so
/usr/share/
/usr/share/doc/
/usr/share/doc/ruby-lapack/
/usr/share/doc/ruby-lapack/README.rdoc
/usr/share/doc/ruby-lapack/changelog.Debian.gz
/usr/share/doc/ruby-lapack/copyright
/usr/share/doc/ruby-lapack/examples/
/usr/share/doc/ruby-lapack/examples/dpotrf.rb
/usr/share/doc/ruby-lapack/examples/dsyevr.rb
/usr/share/rubygems-integration/
/usr/share/rubygems-integration/2.5.0/
/usr/share/rubygems-integration/2.5.0/specifications/
/usr/share/rubygems-integration/2.5.0/specifications/ruby-lapack-1.8.1.gemspec