LaurentPolynomialRing: incorrect conversion of base ring element and failing conversion between rings

[dkrenn]

sage: P = LaurentPolynomialRing(QQ, 'a, b')
sage: Q = LaurentPolynomialRing(P, 'c, d')
sage: Q(P.0)
c

but the expected result is a as it is with polynomial rings:

sage: P = PolynomialRing(QQ, 'a, b')
sage: Q = PolynomialRing(P, 'c, d')
sage: Q(P.0)
a

2. (In some sense) more generally, conversion between certain laurent polynomial rings (e.g. isomorphic rings) fail. E.g. the following should work

sage: L.<a, b, c, d> = LaurentPolynomialRing(QQ)
sage: M = LaurentPolynomialRing(QQ, 'c, d')
sage: Mc, Md = M.gens()
sage: N = LaurentPolynomialRing(M, 'a, b')
sage: Na, Nb = N.gens()
sage: M(c/d)
sage: N(a*b/c/d)
sage: N(c/d)
sage: L(Mc)
sage: L(Nb)

3. As needed to fix the above, a method is_constant, as well as methods for the conversions of constant laurent polynomials are to be implemented.

Depends on #21833

CC: @cheuberg

Component: algebra

Author: Daniel Krenn

Branch/Commit: 65e2fc5

Reviewer: Frédéric Chapoton, Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/21855

[dkrenn]

Description changed:

--- 
+++ 
@@ -2,7 +2,7 @@
 ```
 sage: P = LaurentPolynomialRing(QQ, 'a, b')
 sage: Q = LaurentPolynomialRing(P, 'c, d')
-sage: Q(P.gens()[0])
+sage: Q(P.0)
 c
 ```
 but the expected result is `a` as it is with polynomial rings:
@@ -10,6 +10,6 @@
 ```
 sage: P = PolynomialRing(QQ, 'a, b')
 sage: Q = PolynomialRing(P, 'c, d')
-sage: Q(P.gens()[0])
+sage: Q(P.0)
 a
 ```

[dkrenn]

Branch: u/dkrenn/laurent-uni-convert

[dkrenn]

Author: Daniel Krenn

[dkrenn]

Commit: a5f7483

[dkrenn]

Description changed:

--- 
+++ 
@@ -13,3 +13,18 @@
 sage: Q(P.0)
 a
 ```
+(In some sense) more generally, conversion between certain laurent polynomial rings (e.g. isomorphic rings) fail. E.g. the following should work
+
+```
+sage: L.<a, b, c, d> = LaurentPolynomialRing(QQ)
+sage: M = LaurentPolynomialRing(QQ, 'c, d')
+sage: Mc, Md = M.gens()
+sage: N = LaurentPolynomialRing(M, 'a, b')
+sage: Na, Nb = N.gens()
+sage: M(c/d)
+sage: N(a*b/c/d)
+sage: N(c/d)
+sage: L(Mc)
+sage: L(Nb)
+```
+

[dkrenn]

comment:3

Let's see what the patchbot says...

---

Last 10 new commits:

cbe45b0	is_constant for laurent polynomials
7dc0fbc	conversion to integer/rationals for constant laurent polynomials
d1b30ee	test conversion to QQ and ZZ (and refine method definition to allow this)
0168003	minor rewrite wrt to ETuple
a809ca5	splitting helper _split_laurent_polynomial_dict_
abe194b	convert multivariate laurent polynomial
7660d73	minor code rewrites in _split_laurent_polynomial_dict_
2dc2e98	docstring of _split_laurent_polynomial_dict_
02ae8e7	conversion of univariate laurent polynomial rings and doctests
a5f7483	rewrite parts of the element construction to handle conversions to the base ring better

[dkrenn]

Description changed:

--- 
+++ 
@@ -1,3 +1,4 @@
+1.
 
 ```
 sage: P = LaurentPolynomialRing(QQ, 'a, b')
@@ -13,7 +14,7 @@
 sage: Q(P.0)
 a
 ```
-(In some sense) more generally, conversion between certain laurent polynomial rings (e.g. isomorphic rings) fail. E.g. the following should work
+2. (In some sense) more generally, conversion between certain laurent polynomial rings (e.g. isomorphic rings) fail. E.g. the following should work
 
 ```
 sage: L.<a, b, c, d> = LaurentPolynomialRing(QQ)
@@ -27,4 +28,4 @@
 sage: L(Mc)
 sage: L(Nb)
 ```
-
+3. As needed to fix the above, a method `is_constant`, as well as methods for the conversions of constant laurent polynomials are to be implemented.

[sagetrac-git]

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

ef8a412	implement LaurentPolynomialRing.variable_names_recursive
9e1c95f	adapt docstring of PolynomialRing.variable_names_recursive
a6f56d3	laurent polynomial converter from symbolic expressions
7226856	adapt docstring
8b4c684	method Expression.laurent_polynomial
ba5f230	create laurent polynomials from symbolic expressions (in LaurentPolynomialRing)
8dba3f5	Merge branch 'u/dakrenn/laurent-symbolic' into u/dkrenn/laurent-uni-convert

[sagetrac-git]

Changed commit from a5f7483 to 8dba3f5