It looks like
f = Function('f')
f.is_real = True
also works, although I wouldn't use it unless you really don't know
the names of the functions you want to create until runtime.
Aaron Meurer
On Tue, Feb 24, 2015 at 5:31 PM, Aaron Meurer <[email protected]> wrote:
> On Tue, Feb 24, 2015 at 4:51 PM, John Peterson <[email protected]> wrote:
>>
>>
>> On Tuesday, February 24, 2015 at 3:15:03 PM UTC-7, Aaron Meurer wrote:
>>>
>>> The problem is that assumptions on Function don't do anything
>>> (https://github.com/sympy/sympy/issues/6494). If you want to create a
>>> Function with assumptions, you'll need to subclass Function
>>> explicitly, like
>>>
>>> class f(Function):
>>> is_real = True
>>
>>
>> Thanks for pointing out the real issue! I tried to implement your
>> suggestion, but I'm not a particularly skillful python programmer, so my
>> first attempt at subclassing Function in the way you described didn't
>> work...
>>
>> Here's the code:
>>
>>> #!/usr/bin/env python
>>> from sympy import *
>>> class real_function(Function):
>>> is_real=True
>>> X = Symbol('X', real=True)
>>> f = real_function('f')(X)
>>> g = real_function('g')(X)
>>> print diff (abs(f-g), X)
>
> It would just be real_function(X).
>
> "Function('f')" is (roughly) the same as "class f(Function): pass".
> That is, it creates a subclass of Function called f. You will need to
> create a new subclass for each function. Clearly, that's not super
> easy to do if you want to create them on the fly, which is why we
> should fix that issue.
>
> Aaron Meurer
>
>>
>>
>> And the error message:
>>
>>> Traceback (most recent call last):
>>> File "testcase.py", line 10, in <module>
>>> f = real_function('f')(X)
>>> TypeError: 'real_function' object is not callable
>>
>>
>> which I don't understand how to fix.
>>
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