#19388: Write better doctest for parent.register_embedding
---------------------------+----------------------------
Reporter: nbruin | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.9
Component: misc | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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One of the current doctests on parent.register_embedding doesn't actually
do what it should:
{{{
sage: x = QQ['x'].0
sage: t = abs(ZZ.random_element(10^6))
sage: K = NumberField(x^2 + 2*3*7*11, "a"+str(t))
sage: a = K.gen()
sage: K_into_MS = K.hom([a.matrix()])
sage: K._unset_coercions_used()
sage: K.register_embedding(K_into_MS)
sage: L = NumberField(x^2 + 2*3*7*11*19*31,
"b"+str(abs(ZZ.random_element(10^6))))
sage: b = L.gen()
sage: L_into_MS = L.hom([b.matrix()])
sage: L._unset_coercions_used()
sage: L.register_embedding(L_into_MS)
sage: a * b.matrix()
[this shouldn't test a registered embedding at all]
}}}
The problem here is that there is an "action" defined of `K` on
`parent(b.matrix())` (namely, scalar multiplication on the base changed
matrix) and actions are supposed to be discovered before coercions are, as
documented on, e.g. `get_coercion_model().bin_op`. Previously, action
discovery failed with an embedding map that produces unhashable elements,
so the test above would use the registered embedding due to a covered up
unexpected error. So the test only accidentally had anything to do with
the registered embedding. With #19016 this is no longer the case. Can we
replace this test with something more sensible? (also, note that anything
calling `_unset_coercions_used` is a hack).
--
Ticket URL: <http://trac.sagemath.org/ticket/19388>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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