A parser that helps contract the creation/annihilation operators with phase factor.
This repository follows the style of numpy's einsum function that automatically parses the symbols in a string.
It implements the Wick's theorem, taking good care of the phase factor for each term, with consideration to the
occupied / virtual orbitals during the contraction. The symbols follow the convention of
"a", "b", .... -> virtual
"i", "j", .... -> occupied
"p", "q", .... -> general
which can also be customized.
Should be good to go directly running the unit test, after exporting- the directory to this repository- to $PYTHONPATH.