#17445: Missing documentation of derivative operator/notation
-------------------------------+------------------------
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 schymans):
Replying to [comment:6 nbruin]:
> The fact that `function('f')` and `function('f',x)` return different
types of arguments is '''really''' bad. It prevents any convincing
explanation of the distinction that is essential here, because the
interface ''itself'' confuses the two different issues. On top of that, we
have a lot of documentation that was written by people who were equally
confused, so the calculus doc makes a good effort to confuse any new user
too.
Wow, the reason while I hesitated about adding documentation of the
D-notation was that I thought it should go into the documentation of
function() and then I found out that the documentation of function()
itself is already incomplete and confusing. Should we open a ticket for
that, too?
For example, none of the methods described in
http://www.sagemath.org/doc/reference/calculus/sage/symbolic/function_factory.html
show up when I type:
{{{
function?
}}}
The distinction between
{{{
f = function('f')
}}}
and
{{{
f = function('f', x)
}}}
is also not documented.
Only now I realised that function('f') returns a function, while
function('f',x) returns an expression. Furthermore, differentiation of a
function is not supported, it needs to be converted to an expression
first:
{{{
f = function('f')
fx = function('f', x)
print type(f)
print type(fx)
print type(f(x))
print fx.diff()
print f(x).diff()
print f.diff()
///
<class 'sage.symbolic.function_factory.NewSymbolicFunction'>
<type 'sage.symbolic.expression.Expression'>
<type 'sage.symbolic.expression.Expression'>
D[0](f)(x)
D[0](f)(x)
Traceback (most recent call last): print f(x).diff()
File "", line 1, in <module>
File "/tmp/tmpMe44Jp/___code___.py", line 9, in <module>
exec compile(u'print f.diff()' + '\n', '', 'single')
File "", line 1, in <module>
AttributeError: 'NewSymbolicFunction' object has no attribute 'diff'
}}}
>
> It's an entirely different issue, though. Apparently the documentation
never ''explains'' what `D[0](f)(x)` means. We can do that independent of
whether we go out of our way to confuse users about the distinction
between functions and functions evaluated at ...
If we modify the documentation of diff(), though, we should explain why
f(x).diff() works but f.diff() does not.
--
Ticket URL: <http://trac.sagemath.org/ticket/17445#comment:8>
Sage <http://www.sagemath.org>
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