I contributed to the open source deal.ii C++ library by adding functionality to its interface with the Trilinos library and also added unit test to testing-suite. Specifically, I added the ability to use direct solvers for large-scale distributed linear systems (using MPI) without the need to re-factorize the matrix every time a solve is performed. This functionality was immediately adopted by users and resulted in improved runtimes which were a 250x faster in my case.