#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:12 kcrisman]:
> Questions:
> * Is it worth trying to distinguish `D[0,1]` and `D[1,0]`?
I think not, but it's not my field. When do you really work with non-
continuously differentiable functions? Don't you use distributions then
anyway? I think someone should point out a meaningful calculation where
symmetry doesn't hold.
> * Would it be very hard to do so? (I have not looked at this code in a
long time.)
No. It's in the `diff` code somewhere. It's probably an explicit "sort"
command you can just take out.
> * Alternately (or with that), would it be possible to just "read off"
the actual variable names and put those in, ala `D[x,y]` and `D[y,x]`? In
principle it should be, since all such functions now have ''ordered''
variable names.
Where would you get the names from in the following example?
{{{
sage: D=sage.symbolic.operators.FDerivativeOperator
sage: D(f,[0,1,0])
D[0, 1, 0](f)
sage: D(f,[0,1,0])(x,y)
D[0, 0, 1](f)(x, y)
}}}
If you're going to bother matching indices and variable names, you'd
better go the whole way and recognize that in the last example the
arguments are distinct symbolic variables that match up nicely with the
differentiation indices, so we can print
{{{
diff(f(x,y),x,x,y)
}}}
I don't know how that would combine with the whole `D[0,1](f)(x,x+1)`
thing, so maybe it's a bad idea.
--
Ticket URL: <http://trac.sagemath.org/ticket/17445#comment:16>
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