* 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>
`error = abs(f(a))` was declared on line 24 and line 32. It is unnecessary to have in both places.
I removed the second instance since it wastes resources to keep redefining the variable inside the for loop.
This fixes an [issue found by lgtm](66c4afbd0f/files/maths/newton_raphson.py)