StringifyMapper: Incorrect result for side-by-side product nodes
kaushikcfd opened this issue · comments
>>> import pymbolic.primitives as p
>>> a = p.Variable("a")
>>> b = p.Variable("b")
>>> c = p.Variable("c")
>>> print(a * (b * c))
a*b*c # Should have been 'a*(b*c)'
Pymbolic flattens those, assuming that multiplication is associative. (Product can have multiple children.) Do you have a use case in which that's not correct behavior?
Pymbolic flattens those,
The AST is correct (i.e. unflattened) but I think the StringifyMapper is to be blamed here.:
>>> a * (b * c)
Product((Variable('a'), Product((Variable('b'), Variable('c')))))Do you have a use case in which that's not correct behavior?
No, no concrete use case.
No, no concrete use case.
Well given floating point arithmetic is not associative we can always buggy behavior associated with this in a generated code ;).
Well given floating point arithmetic is not associative we can always buggy behavior associated with this in a generated code ;).
Grr, you're right. We should probably turn off auto-flattening. #69
For the StringifyMapper, I can think of use cases where I'd want the parentheses and where I wouldn't. (Math vs CS, really.) Would an option be OK?
I can think of use cases where I'd want the parentheses and where I wouldn't. (Math vs CS, really.) Would an option be OK?
I think its unsafe to stringify to incorrect schedules and should be avoided.
Would an option be OK?
Yep, but the default should prefer correctness.
OK, I can live with that.
I think it is not just StringifyMapper that is wrong, even the parser implements left-to-right associativity incorrectly:
>>> parse("a*b*c")
Product((Variable('a'), Product((Variable('b'), Variable('c')))))
>>> from pymbolic.mapper.evaluator import evaluate
>>> a_np = np.float64(1/3)
>>> b_np = np.finfo("float64").max
>>> c_np = np.float64(2)
>>> a_np * b_np * c_np
1.1984620899082103e+308
>>> evaluate(parse("a*b*c"), {"a": a_np, "b": b_np, "c": c_np})
/home/line/.local/lib/python3.10/site-packages/pytools/__init__.py:1103: RuntimeWarning: overflow encountered in double_scalars
return reduce(mul, iterable, 1)
inf