Infinite matrix groups over QQ fail for is_finite()

[rbeezer]

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?

CC: @videlec

Component: algebra

Author: Frédéric Chapoton

Branch/Commit: 9892a36

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/8550

[loefflerd]

comment:1

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).

[fchapoton]

Author: Frédéric Chapoton

[fchapoton]

New commits:

9892a36

trac 8550 fix order of SL(2,QQ)

[fchapoton]

Commit: 9892a36

[fchapoton]

Branch: u/chapoton/8550

[fchapoton]

comment:3

green bot, please review

[tscrim]

comment:4

LGTM.

[tscrim]

Reviewer: Travis Scrimshaw

[fchapoton]

comment:5

thanks

[vbraun]

Changed branch from u/chapoton/8550 to 9892a36