sympy/sympy — pull request #1495 by amakelov (2012-08-17 12:41:22+00:00)
Title: [Work in progress] Centralizers, improved normal closure & applications

Implemented an algorithm to compute centralizers of groups/subsets/elements within other groups, using a backtrack search .subgroup_search().

Improved the normal closure algorithm with some randomization, and added some applications - the derived and lower central series, nilpotency testing, etc.

Changed the file structure a bit by introducing some new files: sympy/combinatorics/group_constructs.py, which will host functions treating several groups equally, such as DirectProduct, and sympy/combinatorics/testutil.py which will host utility functions used exclusively for testing purposes (such as _verify_bsgs).

Currently I only have to write tests for the new functions in testutil.py and improve the style a bit.