* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
* Create newton_forward_interpolation.py
This code is for calculating newton forward difference interpolation for fixed difference.
* Add doctests and reformat with black