Opened 12 years ago

Closed 5 years ago

#8550 closed defect (fixed)

Infinite matrix groups over QQ fail for is_finite()

Reported by: rbeezer Owned by: AlexGhitza
Priority: minor Milestone: sage-8.2
Component: algebra Keywords:
Cc: vdelecroix Merged in:
Authors: Frédéric Chapoton Reviewers: Travis Scrimshaw
Report Upstream: N/A Work issues:
Branch: 9892a36 (Commits, GitHub, GitLab) Commit: 9892a36fe40dc681a3f5c00e278b200878a450ac
Dependencies: Stopgaps:

Status badges

Description

sage: H=SL(2,QQ)
sage: H.is_finite()
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)

/sage/dev/<ipython console> in <module>()

/sage/dev/local/lib/python2.6/site-packages/sage/groups/matrix_gps/matrix_group.pyc in is_finite(self)
    343         if self.base_ring().is_finite():
    344             return True
--> 345         return self._gap_().IsFinite().bool()
    346
    347     def cardinality(self):

/sage/dev/local/lib/python2.6/site-packages/sage/groups/matrix_gps/matrix_group.pyc in _gap_(self, G)
    217             return SageObject._gap_(self, G)
    218         except TypeError:
--> 219             raise NotImplementedError, "Matrix group over %s not implemented."%self.__R
    220
    221     def __cmp__(self, H):

NotImplementedError: Matrix group over Rational Field not implemented.

GL fails similarly. Other rings (ZZ, finite fields) seem to work OK, so perhaps this is restricted to something peculiar to the rationals?

Change History (6)

comment:1 Changed 12 years ago by davidloeffler

From the Gap manual, I get the impression that Gap won't allow you to construct a group unless it is finitely generated (and it knows how to calculate a set of generators). That's why Gap will allow you to work with GL(2, ZZ) but not GL(2, QQ).

comment:2 Changed 5 years ago by chapoton

  • Authors set to Frédéric Chapoton
  • Branch set to u/chapoton/8550
  • Cc vdelecroix added
  • Commit set to 9892a36fe40dc681a3f5c00e278b200878a450ac
  • Status changed from new to needs_review

New commits:

9892a36trac 8550 fix order of SL(2,QQ)

comment:3 Changed 5 years ago by chapoton

green bot, please review

comment:4 Changed 5 years ago by tscrim

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

LGTM.

comment:5 Changed 5 years ago by chapoton

  • Milestone set to sage-8.2

thanks

comment:6 Changed 5 years ago by vbraun

  • Branch changed from u/chapoton/8550 to 9892a36fe40dc681a3f5c00e278b200878a450ac
  • Resolution set to fixed
  • Status changed from positive_review to closed
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