#19603: Quotient of incompatible lattices
-------------------------------------+-------------------------------------
Reporter: mjo | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.10
Component: geometry | Resolution:
Keywords: | Merged in:
Authors: Andrey | Reviewers: Michael Orlitzky
Novoseltsev | Work issues:
Report Upstream: N/A | Commit:
Branch: | 3c1cb53843a3582a6dc5808c89c81bb30011c960
u/mjo/ticket/19603 | Stopgaps:
Dependencies: |
-------------------------------------+-------------------------------------
Changes (by mjo):
* reviewer: => Michael Orlitzky
* branch: u/novoselt/quotient_of_incompatible_lattices =>
u/mjo/ticket/19603
* commit: 399bc7383ab3ac9edbffd4f21f5dd9cb3fd9b86c =>
3c1cb53843a3582a6dc5808c89c81bb30011c960
Comment:
I added some tests/examples to the `quotient` method but noticed something
strange when I went to do the same for the `ToricLattice_quotient` class.
The code in the class calls `submodule()` which is where the error is
expected to occur:
{{{
if check:
try:
W = V.submodule(W)
except (TypeError, ArithmeticError):
raise ArithmeticError("W must be a sublattice of V")
}}}
But the `submodule()` method isn't throwing one of those two errors --
it's throwing a `ValueError`. The result is that the user sees the
exception thrown from `submodule()` and not the (nicer) error from the
quotient class:
{{{
sage: from sage.geometry.toric_lattice import ToricLattice_quotient
sage: N = ToricLattice(3)
sage: M = ToricLattice(3, name='M')
sage: ToricLattice_quotient(N,M)
...
ValueError: M(1, 0, 0) can not generate a sublattice of 3-d lattice N
}}}
For the wishlist, it might help to report something other than the
variable names in the `ToricLattice_quotient` error message. So instead
of,
{{{
ArithmeticError: W must be a sublattice of V
}}}
it could be,
{{{
ArithmeticError: 3-d lattice M must be a sublattice of 3-d lattice N
}}}
but I realize that's hard to do if the user passes in weirder objects. We
could get part of the way there by checking that `V` is in fact a lattice
before doing the `submodule()` check. That way `V` will print nicely, and
even if the user passes in something stupid it would read alright:
{{{
ArithmeticError: Petersen graph: Graph on 10 vertices is not a sublattice
of 3-d lattice N
}}}
----
New commits:
||[http://git.sagemath.org/sage.git/commit/?id=399bc7383ab3ac9edbffd4f21f5dd9cb3fd9b86c
399bc73]||{{{Improve checks for toric lattice span and quotient.}}}||
||[http://git.sagemath.org/sage.git/commit/?id=5f62fd8c978aa67c8de7c554dda4aa1d7644fed9
5f62fd8]||{{{Trac #19603: remove trailing whitespace (review).}}}||
||[http://git.sagemath.org/sage.git/commit/?id=3c1cb53843a3582a6dc5808c89c81bb30011c960
3c1cb53]||{{{Trac #19603: add a few more examples and tests for lattice
quotients (review).}}}||
--
Ticket URL: <http://trac.sagemath.org/ticket/19603#comment:4>
Sage <http://www.sagemath.org>
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