#14982: When a parent is equipped with an embedding, consider coercions that
don't
go through the embedding
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Reporter: mmezzarobba | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.4
Component: coercion | Resolution:
Keywords: embedding | Merged in:
Authors: Marc Mezzarobba, | Reviewers:
Vincent Delecroix | Work issues:
Report Upstream: N/A | Commit:
Branch: | d99564520a5fd599c0fea62b86d0bdbfbd35c1a4
u/mmezzarobba/14982-coerce_embeddings| Stopgaps:
Dependencies: |
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Comment (by vdelecroix):
Hello,
I am not sure I am the best person to do the complete review. But...
1. Is this really the example you wanted to show {{{MatrixSpace(L, 2,
2).coerce_map_from(L)}}}. Wouldn't be better to test {{{MatrixSpace(K, 2,
2).coerce_map_from(L)}}}? Idem for the one with {{{PowerSeriesRing}}} that
follows.
2. With your modifications the following changes. Old version:
{{{
sage: C12.<zeta12> = CyclotomicField(12)
sage: C4.<zeta4> = CyclotomicField(4, embedding=zeta12**3)
sage: PowerSeriesRing(C12, 'x').coerce_map_from(C4)
Composite map:
From: Cyclotomic Field of order 4 and degree 2
To: Power Series Ring in x over Cyclotomic Field of order 12 and
degree 4
Defn: Generic morphism:
From: Cyclotomic Field of order 4 and degree 2
To: Cyclotomic Field of order 12 and degree 4
Defn: zeta4 -> zeta12^3
then
Conversion map:
From: Cyclotomic Field of order 12 and degree 4
To: Power Series Ring in x over Cyclotomic Field of order 12
and degree 4
}}}
Versus new version:
{{{
sage: PowerSeriesRing(C12, 'x').coerce_map_from(C4)
Conversion map:
From: Cyclotomic Field of order 4 and degree 2
To: Power Series Ring in x over Cyclotomic Field of order 12 and
degree 4
sage: timeit("mor(a)", number=5000, repeat=6)
5000 loops, best of 6: 120 µs per loop
}}}
whereas for `PolynomialRing` the behavior is identical (similar to the
"old version" above). Is it the kind of thing that you expected?
Vincent
--
Ticket URL: <http://trac.sagemath.org/ticket/14982#comment:56>
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