On Fri, Mar 27, 2015 at 5:26 PM, Joachim Durchholz <[email protected]> wrote:
> Am 24.03.2015 um 22:29 schrieb Aaron Meurer:
>>
>> On Tue, Mar 24, 2015 at 4:36 AM, Joachim Durchholz <[email protected]>
>> wrote:
>>>
>>> Is Meijer heuristic? In that case, I think variation due to changed sort
>>> order would be expected.
>>
>>
>> Yes, it uses a lot of pattern matching, which is heuristic in nature.
>
>
> I have tracked down the difference to a flatten() call inside the Mul
> constructor. After that, Meijer is getting its heuristics in a different
> order.
> (I have taken a cursory look at the other test failures, and ~75% seem to be
> integration-heavy math such as quantum physics.)
>
> Problem is that if we change Mul to not sort its arguments via flatten, this
> is going to ripple all over SymPy. That's not a labyrinth I wish to enter.
> (1)
>
> The other approach would be to accept that some unit tests depend on sort
> order in a superficial way, and to change the unit tests. (2)

Is the result deterministic?  And is it still mathematically correct?

Aaron Meurer

>
> Is there a third, better approach?
>
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