#2562: [with patch, needs review] minor symbolic doc things
-------------------------+--------------------------------------------------
Reporter: zimmerma | Owner: was
Type: enhancement | Status: new
Priority: minor | Milestone: sage-4.1.2
Component: calculus | Keywords:
Reviewer: | Author:
Merged: |
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Comment(by burcin):
The use of the word `inexact` in Sage is misleading in general, and there
are further problems when talking about elements of the `Symbolic Ring`.
AFAIK, Sage regards any element of RR, CC, etc. as inexact. Since `1.9393`
is by default in RR, we say that it's inexact. E.g.,
{{{
sage: t = 1.9393
sage: t.parent()
Real Field with 53 bits of precision
sage: RR
Real Field with 53 bits of precision
sage: t.parent() is RR
True
}}}
Being `inexact` is a property of a ring, which you test with the
`.is_exact()` function. The new `Symbolic Ring` can have arbitrary python
objects as elements, so it could in theory have exact members too.
However, to cover all cases, it reports that it is inexact:
{{{
sage: SR.is_exact()
False
}}}
Maybe in the future we'll move this exactness check to the element level,
at least for polynomials, matrices etc. over `SR`, since in many cases it
prevents using more efficient algorithms.
The problem reported on line 582 of the old `calculus.py` has moved to
line 403 of `sage/symbolic/ring.pyx`. Paul, do you have any suggestions on
how to improve the documentation (especially around the place you
mentioned) with regards to this issue?
----
Most of the problems pointed out by this ticket don't exist in the new
symbolics code, so I would be ok with addressing the two issues in
attachment:trac_2562-minor-symb-docs.patch) and closing this ticket.
Though, I am still not comfortable with the wording here:
{{{
Return True if this symbolic expression does not evaluate to
(symbolic) zero.
}}}
I suggest something like
{{{
Return True unless this symbolic expression can be shown to be
zero.
Note that deciding if an expression is zero is undecidable in
general.
}}}
It would be better to write more on how the function tests for zero, and
explain that there could be cases where it returns `True` for an
expression equal to zero (though I couldn't think of an example right
now), but I'm willing to give this a positive review with the minor
improvement I suggest above.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/2562#comment:2>
Sage <http://sagemath.org/>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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