Fix coercions and pushout for Laurent series

[videlec]

There should be an automatic extension of scalars in the following situation

sage: R.<x> = LaurentSeriesRing(QQ)
sage: QQbar.gen() * x
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for *: 'Algebraic Field' and
'Laurent Series Ring in x over Rational Field'

To be compared with

sage: R.<x> = PowerSeriesRing(QQ)
sage: QQbar.gen() * x
I*x
sage: parent(_)
Power Series Ring in x over Algebraic Field

Currently, these pushouts are allowed:

sage: x = LaurentSeriesRing(QQ, 'x').gen()
sage: y = PolynomialRing(QQ, 'y').gen()
sage: x * y
x*y
sage: parent(x * y)
Univariate Polynomial Ring in y over
Laurent Series Ring in x over Rational Field

This is inconsistent with PowerSeriesRing.

By fixing these problems, we had to adapt some code in sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py that was using the aforementioned pushout.

Depends on #24420

Component: algebra

Author: Vincent Delecroix

Branch/Commit: 8abc33b

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/24431

[videlec]

Branch: u/vdelecroix/24431

[videlec]

New commits:

f779b10	24420: clean laurent series
eb2bba4	24431: pushout for Laurent series

[videlec]

Commit: eb2bba4

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

1adb84c	24420: clean laurent series
27f324e	24431: pushout for Laurent series

[sagetrac-git]

Changed commit from eb2bba4 to 27f324e

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

cdf836a	24420: clean laurent series
00deb27	24431: pushout for Laurent series

[sagetrac-git]

Changed commit from 27f324e to 00deb27

[sagetrac-git]

Changed commit from 00deb27 to c905ee9

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

f95f61e	24413: make polynomial rings know that they are infinite
c905ee9	24413: base ring = 0

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

cdf836a	24420: clean laurent series
00deb27	24431: pushout for Laurent series

[sagetrac-git]

Changed commit from c905ee9 to 00deb27

[sagetrac-git]

Changed commit from 00deb27 to 1b1bbbc

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

1b1bbbc

24431: Laurent series pushout and coercions

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

34769e1	24420: clean laurent series
b3f11d9	24431: Laurent series pushout and coercions

[sagetrac-git]

Changed commit from 1b1bbbc to b3f11d9

[videlec]

comment:10

rebased on 8.2.beta2

[tscrim]

comment:11

LGTM except I don't understand the non-import changes in schemes/hyperelliptic_curves/hyperelliptic_generic.py. (Also, is LaurentPolynomialRing is not used in that file.)

[videlec]

comment:12

Replying to @tscrim:

LGTM except I don't understand the non-import changes in schemes/hyperelliptic_curves/hyperelliptic_generic.py. (Also, is LaurentPolynomialRing is not used in that file.)

I believe you refer to this line

-    L = PolynomialRing(self.base_ring(),'x')
+    L = PolynomialRing(K,'x')

This is the third point in the ticket description.

[tscrim]

comment:13

I understand now the reason why that change is needed. Thanks. (Although I don't quite understand why that pushout is no longer allowed, but that's okay.)

Just remove the unneeded import of LaurentPolynomialRing and the \'s here

@@ -410,7 +565,11 @@ class LaurentSeriesRing_generic(UniqueRepresentation, ring.CommutativeRing):
 
         from sage.rings.polynomial.polynomial_ring import is_PolynomialRing
         from sage.rings.power_series_ring import is_PowerSeriesRing
-        if ((is_LaurentSeriesRing(P) or is_PowerSeriesRing(P) or is_PolynomialRing(P))
+        from sage.rings.polynomial.laurent_polynomial_ring import is_LaurentPolynomialRing
+        if ((is_LaurentSeriesRing(P) or \
+             is_LaurentPolynomialRing(P) or \
+             is_PowerSeriesRing(P) or \
+             is_PolynomialRing(P))
             and P.variable_name() == self.variable_name()
             and A.has_coerce_map_from(P.base_ring())):
             return True

and you can set a positive review on my behalf.

[tscrim]

Reviewer: Travis Scrimshaw

[sagetrac-git]

Changed commit from b3f11d9 to de63301

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

de63301

24431: unneeded '\' and more tests

[videlec]

comment:15

I did not find the import you were talking about in [comment:13].

[tscrim]

comment:16

diff --git a/src/sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py b/src/sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py
index cdca282..9e9897a 100644
--- a/src/sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py
+++ b/src/sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py
@@ -33,7 +33,11 @@ from __future__ import absolute_import
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
 
-from sage.rings.all import PolynomialRing, RR, PowerSeriesRing, LaurentSeriesRing, O
+from sage.rings.polynomial.all import PolynomialRing, LaurentPolynomialRing
+from sage.rings.big_oh import O
+from sage.rings.power_series_ring import PowerSeriesRing
+from sage.rings.laurent_series_ring import LaurentSeriesRing
+from sage.rings.real_mpfr import RR
 from sage.functions.all import log
 from sage.structure.category_object import normalize_names
 

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

cd4b485

24431: remove unused import

[sagetrac-git]

Changed commit from de63301 to cd4b485

[mezzarobba]

comment:18

Looks like there is a test failure since 8.2.beta3.

[tscrim]

comment:19

It is trivial due to the output of the functor. Once fixed, you can set a positive review on my behalf.

[sagetrac-git]

Changed commit from cd4b485 to 8abc33b

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

8abc33b

24431: Laurent series pushout and coercions

[videlec]

comment:21

Rebased on beta4. Waiting for patchbots as an extra check.

[vbraun]

Changed branch from u/vdelecroix/24431 to 8abc33b