#13299: Improve slice and __getitem__ methods of padics
------------------------+---------------------------------------------------
Reporter: saraedum | Owner: roed
Type: defect | Status: new
Priority: minor | Milestone: sage-5.3
Component: padics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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There are a few surprises/bugs in the way that slices and
{{{__getitem__}}} works for padics.
* Slices are not supported in some cases:
{{{
sage: R = Zp(5, 6, 'capped-rel')
sage: a = R(1/2); a
3 + 2*5 + 2*5^2 + 2*5^3 + 2*5^4 + 2*5^5 + O(5^6)
sage: a[0:5]
ValueError: due to limitations in Python 2.5, you must call the slice()
function rather than using the [:] syntax in this case
}}}
* The precision is sometimes wrong over fields:
{{{
sage: K = Qp(5, 6)
sage: a = K(1/25); a
5^-2 + O(5^4)
sage: a.slice(2, 4)
O(5^6)
}}}
* Over fields, the coefficients are sometimes wrong:
{{{
sage: a.slice(-5, -1)
5^-5 + O(5)
}}}
* Some indices produce an error, even though they are inside the
precision:
{{{
sage: a.precision_absolute()
4
sage: a[0]
IndexError: list index out of range
}}}
* The returned values are sometimes padics
{{{
sage: a = K(1/5 + 5); a
5^-1 + 5 + O(5^5)
sage: a[-2].parent()
5-adic Field with capped relative precision 6
sage: a[-1].parent()
Integer Ring
}}}
* They do not seem to work over unramified extensions. This will be the
topic of a followup ticket.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13299>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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