On Apr 1, 2:34 pm, Michael Orlitzky <mich...@orlitzky.com> wrote:
> Substitution doesn't even work pre-evaluation:
>
> sage: f = function('f', x)
> sage: f_prime = f.diff(x)
> sage: g = function('g', x)
> sage: f_prime.substitute_function(f,g)
> D[0](f)(x)
That's because you're trying to substitute expressions, not functions:
sage: f,g
(f(x), g(x))
For that, you would have to use a different substitution function and
it wouldn't have any effect anyway because the expression f(x) does
not occur in f_prime.
If you fix this, the substitution does work:
sage: f = f.operator()
sage: g = g.operator()
sage: f,g
(f, g)
sage: f_prime.substitute_function(f,g)
D[0](g)(x)
There is a different issue, which is fixed by
http://trac.sagemath.org/sage_trac/ticket/12801
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