#15303: Coercion discovery fails to be transitive
-------------------------------------+-------------------------------------
Reporter: nbruin | Owner:
Type: defect | Status: needs_work
Priority: major | Milestone: sage-5.13
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: Simon King | Reviewers:
Report Upstream: N/A | Work issues: analyse recursion
Branch: | error
u/SimonKing/ticket/15303 | Commit:
Dependencies: #14711 | f837cbee8f81c4946a92193c73e86449c53515d9
| Stopgaps:
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Comment (by SimonKing):
Aha! As it turns out, the "coerce costs" of the direct map are higher than
the coerce costs of the composite map that goes via the universal
cyclotomic field:
{{{
sage: UCF.<E> = UniversalCyclotomicField()
sage: psi = QQbar.coerce_map_from(ZZ)
sage: psi._coerce_cost
30
}}}
versus
{{{
sage: psi = QQbar.coerce_map_from(ZZ)
sage: psi._coerce_cost
100
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/15303#comment:24>
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