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. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy?hl=en -~----------~----~----~----~------~----~------~--~---