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).
Ronan
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