#9940: Fix equality/inequality for AdditiveAbelianGroup
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Reporter: mpatel | Owner: joyner
Type: defect | Status: needs_work
Priority: critical | Milestone: sage-4.6.1
Component: group theory | Keywords:
Author: John Palmieri | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Changes (by jhpalmieri):
* status: needs_review => needs_work
Comment:
Replying to [comment:11 mpatel]:
> It seems the only other class that derives [directly] from
`FGP_Module_class` is `sage.geometry.toric_lattice.ToricLattice_quotient`,
which also doesn't define its own `__eq__` and `__ne__`:
{{{
#!python
sage: N1 = ToricLattice(3)
sage: sublattice1 = N1.submodule([(1,1,0), (3,2,1)])
sage: Q1 = N1/sublattice1
sage: N2 = ToricLattice(3)
sage: sublattice2 = N2.submodule([(1,1,0), (3,2,1)])
sage: Q2 = N2/sublattice2
sage: Q1 == Q2
True
sage: Q1 != Q2
True
}}}
> Is this expected?
I think what I find the most confusing is that comparisons work well for
finitely generated free modules, but not for the derived classes. If they
behaved badly in all cases, I would know how to fix it, and while adding a
{{{__ne__}}} method for `FGP_Module_class` (and perhaps `__lt__` and
`__gt__` methods, although I'm not sure what they should return: I suppose
`self.is_submodule(other) and self != other`) would probably make the
comparisons work, I still wouldn't understand why that was the right place
to do it.
So one question is, is the right thing to do to add methods `__ne__`,
`__lt__`, and `__gt__`, and perhaps `__ge__` and `__le__`, to
`FGP_Module_class`?
I'm marking this as "needs work", because we should address comparisons
like `H<G` at the same time as `H!=G`.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9940#comment:12>
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