Opened 3 months ago

Closed 6 weeks ago

#29469 closed enhancement (fixed)

Have method is_unit of QuotientRingElement and PolynomialQuotientRingElement return True in more cases

Reported by: soehms Owned by:
Priority: major Milestone: sage-9.2
Component: commutative algebra Keywords: quotient ring, polynomial, is_unit, invert
Cc: Merged in:
Authors: Sebastian Oehms Reviewers: Travis Scrimshaw
Report Upstream: N/A Work issues:
Branch: 0beccc8 (Commits) Commit: 0beccc8a6aa2d4074241137f6d264a9d1d9f98bb
Dependencies: Stopgaps:

Description

In the case of both classes there are examples where is_unit raises a NotImplementedError even though the answer True could easily be given: 

sage: P.<x,y> = QQ[]
sage: Q = P.quo([1-x*y])
sage: Q.inject_variables()
Defining xbar, ybar
sage: ybar.is_unit()
Traceback (most recent call last):
...
NotImplementedError:

but: 

sage: ~ybar
xbar

or: 

sage: Z16x.<x> = Integers(16)[]
sage: S.<y> =  Z16x.quotient(x^2 + x + 1)
sage: S(3).is_unit()
Traceback (most recent call last):
...
NotImplementedError: The base ring (=Ring of integers modulo 16) is not a field

but: 

sage: Z16x(3).is_unit()
True

This will be improved here. Se also this ​sage-devel thread.

Change History (7)

comment:1 Changed 3 months ago by soehms

  • Branch set to u/soehms/is_unit_quotient_ring_elemnts_29469

comment:2 Changed 3 months ago by soehms

  • Authors set to Sebastian Oehms
  • Commit set to 85afe0a2ba045263981814a4f913dd2ff82fd9ba
  • Status changed from new to needs_review

New commits:

​85afe0a29469: initial

comment:3 Changed 3 months ago by git

  • Commit changed from 85afe0a2ba045263981814a4f913dd2ff82fd9ba to 0beccc8a6aa2d4074241137f6d264a9d1d9f98bb

Branch pushed to git repo; I updated commit sha1. New commits:

​0beccc829469: fix doctest in matrix0

comment:4 Changed 2 months ago by mkoeppe

  • Milestone changed from sage-9.1 to sage-9.2

Moving tickets to milestone sage-9.2 based on a review of last modification date, branch status, and severity.

comment:5 Changed 6 weeks ago by tscrim

  • Reviewers set to Travis Scrimshaw
  • Status changed from needs_review to positive_review

LGTM.

comment:6 Changed 6 weeks ago by soehms

Thanks!

comment:7 Changed 6 weeks ago by vbraun

  • Branch changed from u/soehms/is_unit_quotient_ring_elemnts_29469 to 0beccc8a6aa2d4074241137f6d264a9d1d9f98bb
  • Resolution set to fixed
  • Status changed from positive_review to closed
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