wflynny wrote:
> I noticed that some screwy things happen with symbols depending on how
> you define them. For example
>
> In [2]: x = Symbol('x', commutative = False)
>
> In [3]: x.is_commutative; x._assumptions
> Out[3]: False
> Out[3]: {'comparable': False}
>
> That's fine. But what happens if we add real = True/False:
>
> In [5]: y = Symbol('y', commutative = False, real = True)
>
> In [6]: y.is_commutative; y._assumptions
> Out[6]: False
> Out[6]: {'commutative': True, 'comparable': False, 'complex': True,
> 'imaginary': False, 'real': True}
>
Thanks for the report, but I think this has been reported here
http://code.google.com/p/sympy/issues/detail?id=1384
Anyway, we expect to totally replace assumptions with a new framework
for next release.
> In [7]: y?
> Type: Symbol
> Base Class: <class 'sympy.core.symbol.Symbol'>
> String Form: y
> Namespace: Interactive
> File: c:\python25\lib\site-packages\sympy\core\symbol.py
> Docstring:
> Assumptions::
> real = True
> commutative = True
>
> You can override the default assumptions in the constructor::
> >>> A,B = symbols('AB', commutative = False)
> >>> bool(A*B != B*A)
> True
> >>> bool(A*B*2 == 2*A*B) == True # multiplication by scalars is
> commutative
> True
> Call def: y(self, *args)
>
> Does this mean that the commutative = False is overwritten? I'm not
> really sure what this means. But, you might run into trouble if you
> use the subs() method. I got this error until I removed the real=True
> part from all my symbols.
>
> Traceback (most recent call last):
> File "C:\Documents and Settings\wflynn\My Documents\Python\One-
> magnon Cross-section Calculation\linear_case.py", line 411, in
> <module>
> cross_sect = generate_cross_section(N_atoms,ops,atom)
> File "C:\Documents and Settings\wflynn\My Documents\Python\One-
> magnon Cross-section Calculation\linear_case.py", line 376, in
> generate_cross_section
> arg[i][j] = sub_in(arg[i][j],exp(I*t*A+I*t*B+I*C+I*D),sp.DiracDelta
> (A+B+C+D))
> File "C:\Documents and Settings\wflynn\My Documents\Python\One-
> magnon Cross-section Calculation\sub_in.py", line 18, in sub_in
> new = _walk_it(expression, pattern, replacement, check)
> File "C:\Documents and Settings\wflynn\My Documents\Python\One-
> magnon Cross-section Calculation\sub_in.py", line 82, in _walk_it
> new.insert(new.index(sub),_walk_it(sub, pattern, replacement,
> check))
> File "C:\Documents and Settings\wflynn\My Documents\Python\One-
> magnon Cross-section Calculation\sub_in.py", line 79, in _walk_it
> new.insert(new.index(sub),replacement.subs(v))
> File "C:\Python25\lib\site-packages\sympy\core\basic.py", line 966,
> in subs
> return self._subs_list(sequence)
> File "C:\Python25\lib\site-packages\sympy\core\basic.py", line 1007,
> in _subs_list
> result = result.subs(old, new)
> File "C:\Python25\lib\site-packages\sympy\core\basic.py", line 971,
> in subs
> return self._subs_old_new(old, new)
> File "C:\Python25\lib\site-packages\sympy\core\cache.py", line 85,
> in wrapper
> func_cache_it_cache[k] = r = func(*args, **kw_args)
> File "C:\Python25\lib\site-packages\sympy\core\basic.py", line 980,
> in _subs_old_new
> return self._eval_subs(old, new)
> File "C:\Python25\lib\site-packages\sympy\core\function.py", line
> 204, in _eval_subs
> return Basic._seq_subs(self, old, new)
> File "C:\Python25\lib\site-packages\sympy\core\basic.py", line 1064,
> in _seq_subs
> return self.__class__(*[s.subs(old, new) for s in args])
> File "C:\Python25\lib\site-packages\sympy\core\multidimensional.py",
> line 127, in wrapper
> return f(*args, **kwargs)
> File "C:\Python25\lib\site-packages\sympy\core\cache.py", line 85,
> in wrapper
> func_cache_it_cache[k] = r = func(*args, **kw_args)
> File "C:\Python25\lib\site-packages\sympy\core\function.py", line
> 141, in __new__
> evaluated = cls.eval(*args)
> File "C:\Python25\lib\site-packages\sympy\functions\special
> \delta_functions.py", line 58, in eval
> if arg.is_positive or arg.is_negative:
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 367, in getit
> return self._what_known_about(name)
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 256, in _what_known_about
> a = getattr(self,'_eval_is_'+k)()
> File "C:\Python25\lib\site-packages\sympy\core\add.py", line 252, in
> _eval_is_positive
> if c.is_positive and r.is_positive:
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 367, in getit
> return self._what_known_about(name)
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 279, in _what_known_about
> a = getattr(self,'is_'+pk)
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 367, in getit
> return self._what_known_about(name)
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 282, in _what_known_about
> self._learn_new_facts( ((pk,a),) )
> File "C:\Python25\lib\site-packages\sympy\core\assumptions.py", line
> 341, in _learn_new_facts
> self._assume_rules.deduce_all_facts(facts, base)
> File "C:\Python25\lib\site-packages\sympy\core\facts.py", line 884,
> in deduce_all_facts
> assert new_facts[k] == v, ('inconsitency between
> facts',new_facts,k,v)
> AssertionError: ('inconsitency between facts', {'real': True,
> 'imaginary': False, 'complex': True, 'commutative': True},
> 'commutative', False)
>
> This was conducted on the most recent version of sympy (I downloaded
> it about an hour ago). It's not a big bug but it's something that
> definitely gave me a headache for a couple of hours today.
> >
>
--
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