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}
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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