#15303: Coercion discovery fails to be transitive
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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: Implement
Branch: | backtracking properly
u/SimonKing/ticket/15303 | Commit:
Dependencies: #14711 | 74821fe5409c3104b5d6eb7407a8287d54170df9
| Stopgaps:
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Changes (by SimonKing):
* work_issues: Analyse recursion error => Implement backtracking properly
Comment:
In #12969, I fixed the backtracking algorithm for the discovery of
actions. There, the problem was that the absence of an action was cached
in the middle of backtracking, i.e., even though some paths were
''temporarily'' forbidden, so that an action was easily found after
allowing the paths again.
In the case of coerce maps, the backtracking algorithm is not properly
implemented either. Namely, paths that have already been visited are not
marked as "forbidden". I think this is a severe bug. It is amazing that it
didn't show up before. In any case, it ''must'' be implemented here, since
otherwise we will hardly be able to add the feature that this ticket is
about.
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Ticket URL: <http://trac.sagemath.org/ticket/15303#comment:49>
Sage <http://www.sagemath.org>
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