I like the first way for the fact that it just has 'x' instead of 'x
(t)', but I like the second way because it is simpler and easier to
implement.
Is there a way to redefined how x = Symbol('x')(t) would print? I
guess subclassing would be one option, take care of it there, and then
use the second approach for the auto substitution stuff.
~Luke
On May 27, 4:49 pm, Ondrej Certik <ond...@certik.cz> wrote:
> We discuss this on IRC with Luke and Fabian. Now I understand -- Luke
> wants the result of differentiating not to be instances of
> Derivative() class, but rather some other symbols, e.g it should
> substitute them for symbols at the end.
>
> One way to do it is to subclass the Symbol() class that does the right
> thing, proof of concept is attached. I had to comment out some lines
> in the Function class that were returning 0 immediately if the
> expression didn't depend on "t" (the symbol we are differentiating
> with respect to).
>
> After applying the patch, you get:
>
> $ python t.py
> x'*cos(x)
>
> Another approach may be to create some decorator around Basic.diff()
> or even create a new function diff, along these lines:
>
> ------------
> from sympy import *
>
> t = Symbol("t")
> x = Function("x")(t)
> print "current way:", diff(sin(x), t)
>
> x_diff = Symbol("x'")
> derivs_dict = {x.diff(t): x_diff}
> def diff(a, b):
> return a.diff(b).subs(derivs_dict)
>
> print "new way:", diff(sin(x), t)
> -------------
>
> This prints:
>
> current way: D(x(t), t)*cos(x(t))
> new way: x'*cos(x(t))
>
> Luke, isn't the second approach cleaner? No need to create new classes, etc.
>
> Ondrej
>
> 0001-Proof-of-concept.patch
> 1KViewDownload
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