On Thu, Oct 22, 2009 at 3:43 PM, Ronan Lamy <ronan.l...@gmail.com> wrote:
>
> Le jeudi 22 octobre 2009 à 14:42 -0700, Ondrej Certik a écrit :
>> On Thu, Oct 22, 2009 at 2:34 PM, andy2O <and...@hotmail.com> wrote:
>> >
>> >
>> > Hi all,
>> >
>> > as_coeff_exponent(...) seems to ignore derivatives, as shown below
>> >
>> > Is this behaviour intended? If so I can report it as an issue - but
>> > last time recorded an issue it turned out I just misunderstood atoms
>> > (), so I thought I'd check first here! :)
>>
>> Sure. :)
>>
>> >
>> > Thanks,
>> > andy
>> >
>> >>>> ================================ RESTART
>> >>>> ================================
>> >>>> from sympy import *
>> >>>> var('x')
>> > x
>> >>>> f=Function('f')
>> >>>> d=diff(f(x),x)
>> >>>> d
>> > D(f(x), x)
>> >>>> d.as_coeff_exponent(f(x))
>> > (1, 1)
>>
>> What do you suggest to be a correct answer? I never used
>> as_coeff_exponent inside a derivative.
>>
>> Ondrej
>
> The correct answer is clearly (D(f(x), x), 0), by analogy with
> cos(x).as_coeff_exponent(sin(x)) == (cos(x), 0). So, yes, Andy, you've
> uncovered a real issue.
>
> I think that the fundamental problem here is that there is no object
> representing the derivative of a function (the current Derivative is an
> operation applying to expressions, not functions).
Yes, I think the Derivative should be improved to be able to represent
a general derivative of a function f(x).
Ondrej
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