#13215: Skew polynomials
-------------------------------------+-------------------------------------
Reporter: caruso | Owner: tbd
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-7.3
Component: algebra | Resolution:
Keywords: skew polynomials | Merged in:
Authors: Xavier Caruso | Reviewers: Burcin Erocal
Report Upstream: N/A | Work issues: see comment #25
Branch: | Commit:
u/arpitdm/skew_polynomials | dd5c575e26faaa88140e67c92130085b28e8b0a2
Dependencies: #13214, #13303, | Stopgaps:
#13640, #13641, #13642 |
-------------------------------------+-------------------------------------
Changes (by jsrn):
* commit: 18c7982a3d363ad004760d91e874783eab4c72ae =>
dd5c575e26faaa88140e67c92130085b28e8b0a2
Comment:
One of the bugs in the doctest has to do with failing in the proper manner
when the twist map is not invertible (this is the `TypeError: bad operand
type for unary ~` bug). This is because `self._map ** n` is being called
with negative `n`, which will then try to invert `self._map` using the
unary `~` operator which is not supported by `self._map` of type
`Homomorphism_im_gens`.
But the code was always supposed to fail! The doc-test just expected the
error NotImplementedError, while the error nowadays is this unhelpful
unary-~-stuff.
One solution is therefore simply to catch the strange error and rethrow a
NotImplementedException. The following patch should be put in
`skew_polynomial_ring.py` (the line numbers are not completely correct):
{{{
@@ -534,9 +534,18 @@ class
SkewPolynomialRing_general(sage.algebras.algebra.Algebra,UniqueRepresentat
try:
return self._maps[n]
except KeyError:
- map = self._map**n
- self._maps[n] = map
- return map
+ if n >= 0:
+ map = self._map**n
+ self._maps[n] = map
+ return map
+ else:
+ try:
+ map = self._map**n
+ except TypeError:
+ raise NotImplementedError("Inversion of the twist map
%s" % self._map)
+ self._maps[n] = map
+ return map
+
}}}
Best,
Johan
----
New commits:
||[https://git.sagemath.org/sage.git/commit?id=c6183bcfb9eb863f5052a3d3cd05e35e85a62c29
c6183bc]||{{{Merge branch 'develop' into temp3}}}||
||[https://git.sagemath.org/sage.git/commit?id=dd5c575e26faaa88140e67c92130085b28e8b0a2
dd5c575]||{{{Editing declarations of cython functions so as to make them
compatible.}}}||
--
Ticket URL: <https://trac.sagemath.org/ticket/13215#comment:42>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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