Fix coercions and pushout for Laurent series

[vdelecroix]

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.

[vdelecroix]

New commits:

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

[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

[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

[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

[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

[git]

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

​1b1bbbc

24431: Laurent series pushout and coercions

[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

[vdelecroix]

rebased on 8.2.beta2

[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.)

[vdelecroix]

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]

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.

[git]

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

​de63301

24431: unneeded '\' and more tests

[vdelecroix]

I did not find the import you were talking about in 13.

[tscrim]

src/sage/schemes/hyperelliptic_curves/hyperelliptic_generic.py

@@ -33 +33 @@
 #                  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
 

[git]

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

​cd4b485

24431: remove unused import

[mmezzarobba]

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

[tscrim]

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

[git]

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

​8abc33b

24431: Laurent series pushout and coercions

[vdelecroix]

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