On Apr 19, 8:44 am, smichr <[email protected]> wrote:
> In trying to rebuild an expression piece by piece, I have generated
> the following expression:
>
>
>
> >>> Add(*[Pow(*[y,2],evaluate=True),Mul(*[-1,Pow(*[y,2],evaluate=True)],evaluate=True)],evaluate=True)
> y**2 - y**2
>
> What do I need to do at this point to get it to go to zero?
I think you just hit an obscure bug. Simplifying your testcase gives
this:
In [11]: Add(Pow(y, 2, evaluate=True), Mul(-1, Pow(y, 2)))
Out[11]:
2 2
y - y
In [12]: Add(Pow(y, 2, evaluate=False), Mul(-1, Pow(y, 2)))
---------------------------------------------------------------------------
AttributeError Traceback (most recent call
last)
/home/one/src/sympy/<ipython console> in <module>()
/home/one/src/sympy/sympy/core/cache.pyc in wrapper(*args, **kw_args)
83 except KeyError:
84 pass
---> 85 func_cache_it_cache[k] = r = func(*args, **kw_args)
86 return r
87
/home/one/src/sympy/sympy/core/operations.pyc in __new__(cls, *args,
**assumptions)
29 if len(args)==1:
30 return _sympify(args[0])
---> 31 c_part, nc_part, order_symbols =
cls.flatten(map(_sympify, args))
32 if len(c_part) + len(nc_part) <= 1:
33 if c_part: obj = c_part[0]
/home/one/src/sympy/sympy/core/add.pyc in flatten(cls, seq)
108 newseq.append(Mul(c,s))
109
--> 110 noncommutative = noncommutative or not
s.is_commutative
111
112 # nan
AttributeError: is_commutative
In [13]: Add(Pow(y, 2), Mul(-1, Pow(y, 2)))
Out[13]: 0
The first two results are wrong. I opened an issue for this:
http://code.google.com/p/sympy/issues/detail?id=1907
Vinzent
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