On Tue, Feb 24, 2015 at 3:51 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)
>
>
> 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.
Try this:
In [1]: class f(Function):
...: is_real=True
...:
In [2]: class g(Function):
...: is_real=True
...:
In [3]: X = Symbol('X', real=True)
In [4]: diff(abs(f(X)-g(X)), X)
Out[4]:
⎛d d ⎞
⎜──(f(X)) - ──(g(X))⎟⋅sign(f(X) - g(X))
⎝dX dX ⎠
Ondrej
>
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