#7016: Bizarre results when taking the mod of a p-adic number
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Reporter: jonhanke | Owner: tbd
Type: defect | Status: new
Priority: critical | Milestone: sage-4.1.2
Component: algebra | Keywords: padic, mod, %
Reviewer: | Author: jonhanke
Merged: |
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Comment(by roed):
This is a consequence of the fact that those two elements have different
parents:
{{{
sage: parent(1+O(2^20))
2-adic Ring with capped relative precision 20
sage: parent(Qp(2)(1))
2-adic Field with capped relative precision 20
}}}
Most rings in sage return an element of the same ring when applying the
operation %. The function you want is residue.
{{{
sage: a = Zp(2)(1); b = Qp(2)(1)
sage: a.residue(3), b.residue(3)
(1, 1)
sage: a.residue(3).parent(), b.residue(3).parent()
(Ring of integers modulo 8, Ring of integers modulo 8)
sage: c = Qp(2)(1/2)
sage: c.residue(3)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
ValueError: Element must have non-negative valuation in order to compute
residue.
}}}
There are some tricky questions for % and // and how they relate. A
similar issue bit William this past spring, so maybe we should have a
design discussion about how to solve it. I'm probably not going to be
working on the p-adics this fall though: my advisor wants me to work on my
thesis. ;-)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7016#comment:3>
Sage <http://sagemath.org/>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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