Hi, On 27 May 2011 23:27, Chris Smith <smi...@gmail.com> wrote:
> The reason for the apparent arbitrariness is that Add uses key=hash (for > speed) while Mul uses Basic.compare. It seems we just overlooked Basic.compare in Mul. I git blame sympy/core/mul.py and the line with Basic.compare didn't change since the first commit in git history (2007)). I did a small experiment and changed Basic.compare to hash() in Mul, but SymPy failed miserably (13 test failures and 49 exceptions (mostly series)). This shows that some parts of SymPy expect commutative part of Muls to be in specific order. We say all the time that hashing is fast and comparison methods aren't. But hash() of an expression isn't very different from from as_tuple_tree(), just hash is cached in _mhash. I will perform another experiment and replace key=hash in Add with sorted_key (but with exactly the same caching approach as Basic.__hash__ uses). Lets see how slow it will be and how many failures it will cause. > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to sympy@googlegroups.com. > To unsubscribe from this group, send email to > sympy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > Mateusz -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
