Opened 12 years ago

Closed 12 years ago

#6669 closed defect (fixed)

Homomorphisms from matrix groups don't have to have matrix groups as codomain

Reported by: mraum Owned by: mraum
Priority: major Milestone: sage-4.3
Component: coercion Keywords:
Cc: mhansen, AlexGhitza Merged in: sage-4.3.alpha0
Authors: Martin Raum Reviewers: Robert Bradshaw
Report Upstream: Work issues: add doctests
Branch: Commit:
Dependencies: Stopgaps:

Status badges

Description

This is an error which occurs if one tries to construct coercing from a matrix group into an algebra. The current implementation of homomorphisms with domain a matrix group require the codomain to be a matrix group, too.

/home/martin/sage-4.1_compiled/local/lib/python2.6/site-packages/sage/categories/homset.pyc in Hom(X, Y, cat)
     64     """
     65     if hasattr(X, '_Hom_'):
---> 66         return X._Hom_(Y, cat)
     67 
     68     global _cache

/home/martin/sage-4.1_compiled/local/lib/python2.6/site-packages/sage/groups/matrix_gps/matrix_group.pyc in _Hom_(self, G, cat)
    230             raise NotImplementedError
    231         if not is_MatrixGroup(G):
--> 232             raise TypeError, "G (=%s) must be a matrix group."%G
    233         import homset
    234         return homset.MatrixGroupHomset(self, G)

TypeError: G (=Group algebra of group "General Linear Group of degree 3 over Finite Field of size 7" over base ring Integer Ring) must be a matrix group.

Attachments (2)

trac-6669-matrix_hom.patch (991 bytes) - added by mraum 12 years ago.
trac-6669-2-matrix_hom.patch (1.5 KB) - added by mraum 12 years ago.
Patch with doctests.

Download all attachments as: .zip

Change History (9)

Changed 12 years ago by mraum

comment:1 Changed 12 years ago by mraum

  • Status changed from new to needs_review
  • Summary changed from Homomorphisms from matrix groups don't have to have matrix groups as codomain to [with patch, needs review]Homomorphisms from matrix groups don't have to have matrix groups as codomain

comment:2 Changed 12 years ago by mhansen

  • Cc mhansen added

comment:3 Changed 12 years ago by AlexGhitza

  • Authors set to Martin Raum
  • Cc AlexGhitza added
  • Summary changed from [with patch, needs review]Homomorphisms from matrix groups don't have to have matrix groups as codomain to Homomorphisms from matrix groups don't have to have matrix groups as codomain

comment:4 Changed 12 years ago by AlexGhitza

  • Status changed from needs_review to needs_work
  • Work issues set to add doctests

This looks good, applies cleanly and passes long tests under sage-4.2. I will test on sage-4.2.1 as soon as sage.math binaries are available.

One thing needs to be fixed: please add some doctests with examples of homomorphisms between matrix groups, and from matrix groups to other types of groups. (I do realise that the method patched here did not have doctests to start with.)

Changed 12 years ago by mraum

Patch with doctests.

comment:5 Changed 12 years ago by robertwb

  • Status changed from needs_work to needs_review

Yep, doctests look fine.

comment:6 Changed 12 years ago by robertwb

  • Status changed from needs_review to positive_review

Looks good to me.

comment:7 Changed 12 years ago by mhansen

  • Merged in set to sage-4.3.alpha0
  • Resolution set to fixed
  • Reviewers set to Robert Bradshaw
  • Status changed from positive_review to closed
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