A small library that provides a standard set of environments for writing optimization problems in Latex. You can find the official repository in ctan and the last updated version in github.
If you update your TeX packages (instructions here), you can simply use it by adding to the preamble of your document:
\usepackage{optidef}
If you do not want to update your packages, just download the package from ctan and add it to your project path.