sympy/sympy — pull request #1250 by alxspopov (2012-04-19 10:14:54+00:00)
Title: Paulialgebra fix

Fixed "FIXME don't work for -I*Pauli(2)*Pauli(3)" multiplication problem

Added eval_sigma function to evaluate the product of Pauli matrices and other symbols (with commutative multiply rules)

Added documentation and examples on using round brackets when calculating product of Pauli matrices and symbols (or numbers), or evaluating the obtained expression in terms of sigma matrices.

Another idea to obtain the correct product (needs proper realization using _op_priority attribute):
to calculate the right product of Pauli matrices first rather then left one.

alexandr.s.popov@gmail.com