childprocess

https://github.com/enkessler/childprocess

Ruby

Cross-platform Ruby library for managing child processes.

Matrix#tr

Returns the trace (sum of diagonal elements) of the matrix.
  Matrix[[7,6], [3,9]].trace
    => 16

Source | Google | Stack overflow

Edit

git clone [email protected]:enkessler/childprocess.git
cd childprocess
open

Contribute

# Make a new branch
git checkout -b -your-name--update-docs-Matrix-tr-for-pr

# Commit to git
git add git commit -m "better docs for Matrix#tr"

# Open pull request
gem install hub # on a mac you can `brew install hub`
hub fork
git push <your name> -your-name--update-docs-Matrix-tr-for-pr
hub pull-request

# Celebrate!