#17445: Missing documentation of derivative operator/notation
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Reporter: schymans | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.5
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: schymans | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:10 schymans]:
> I would much prefer this behaviour:
> {{{
> sage: f.diff(x,y) == f.diff(y,x)
> f.diff(x,y) == f.diff(y,x)
> }}}
>
> It would be unambiguous and shorter. What is the advantage of the
D-notation again?
Please write `f(x,y)` there so that it's clear you're differentiating an
expression, not a function:
{{{
sage: var('x,y')
(x, y)
sage: f=function('f')
sage: f.diff(x,y)
AttributeError: 'NewSymbolicFunction' object has no attribute 'diff'
}}}
The advantage is that you can actually represent evaluations of the
derivative:
{{{
sage: f(x,y).diff(x,y).subs(x=2,y=3)
D[0, 1](f)(2, 3)
}}}
Would you propose to print that as the (admittedly shorter) `f.diff(2,3)`?
It's absolutely possible to print `f(x,y).diff(x,y)` for `D[0,1](f)(x,y)`
because at some point we can see we have an expression with an operator
that is an `FDerivativeOperator`, and where the arguments form a list of
distinct symbolic variables. But we have to print `D[0,1](f)(t,t^2)`.
Printing `f.diff(t,t^2)` is just something else entirely.
--
Ticket URL: <http://trac.sagemath.org/ticket/17445#comment:13>
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