gh-38767: polynomials/fix category
    
We put polynomials (and friends) into the category of algebras with
basis.

Dependencies: #38729
    
URL: #38767
Reported by: Martin Rubey
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/categories/additive_magmas.py

@@ -971,8 +971,8 @@ def extra_super_categories(self):
                     [Category of unital magmas]
 
                     sage: C.super_categories()
-                    [Category of unital algebras with basis over Rational Field,
-                     Category of additive magma algebras over Rational Field]
+                    [Category of additive magma algebras over Rational Field,
+                     Category of unital algebras with basis over Rational Field]
                 """
                 from sage.categories.magmas import Magmas
                 return [Magmas().Unital()]

src/sage/categories/algebra_functor.py

@@ -128,7 +128,6 @@
      Category of semigroup algebras over Rational Field,
      ...
      Category of unital magma algebras over Rational Field,
-     ...
      Category of magma algebras over Rational Field,
      ...
      Category of set algebras over Rational Field,

src/sage/categories/map.pyx

@@ -655,9 +655,11 @@ cdef class Map(Element):
             sage: f = R.hom([x+y, x-y], R)
             sage: f.category_for()
             Join of Category of unique factorization domains
-            and Category of commutative algebras
-            over (number fields and quotient fields and metric spaces)
-            and Category of infinite sets
+             and Category of algebras with basis over
+              (number fields and quotient fields and metric spaces)
+             and Category of commutative algebras over
+              (number fields and quotient fields and metric spaces)
+             and Category of infinite sets
             sage: f.category()
             Category of endsets of unital magmas
              and right modules over (number fields and quotient fields and metric spaces)

src/sage/categories/modules.py

@@ -893,7 +893,7 @@ def __init_extra__(self):
                      (Vector space of dimension 2 over Rational Field,
                       Univariate Polynomial Ring in x over Rational Field)
                     sage: A.category()                                                  # needs sage.modules
-                    Category of Cartesian products of vector spaces
+                    Category of Cartesian products of vector spaces with basis
                      over (number fields and quotient fields and metric spaces)
                     sage: A.base_ring()                                                 # needs sage.modules
                     Rational Field

src/sage/interfaces/tab_completion.py

@@ -71,7 +71,7 @@ def completions(s, globs):
          sage: import sage.interfaces.tab_completion as s
          sage: p = x**2 + 1
          sage: s.completions('p.co',globals()) # indirect doctest
-         ['p.coefficients',...]
+         ['p.coefficient',...]
 
          sage: s.completions('dic',globals()) # indirect doctest
          ['dickman_rho', 'dict']

src/sage/rings/lazy_series_ring.py

@@ -1488,10 +1488,14 @@ def __init__(self, base_ring, names, sparse=True, category=None):
             sage: TestSuite(L).run()                                                    # needs sage.libs.singular
             sage: L.category()
             Category of infinite commutative no zero divisors algebras over
-             (unique factorization domains and commutative algebras over
+             (unique factorization domains and algebras with basis over
               (Dedekind domains and euclidean domains
-              and noetherian rings
-              and infinite enumerated sets and metric spaces)
+               and noetherian rings
+               and infinite enumerated sets and metric spaces)
+              and commutative algebras over
+               (Dedekind domains and euclidean domains
+                and noetherian rings
+                and infinite enumerated sets and metric spaces)
               and infinite sets)
 
             sage: L = LazyLaurentSeriesRing(GF(5), 't')

src/sage/rings/polynomial/laurent_polynomial_ring.py

@@ -445,6 +445,8 @@ def __init__(self, R):
         if R.ngens() != 1:
             raise ValueError("must be 1 generator")
         LaurentPolynomialRing_generic.__init__(self, R)
+        from sage.rings.integer_ring import IntegerRing
+        self._indices = IntegerRing()
 
     Element = LaurentPolynomial_univariate
 
@@ -561,6 +563,12 @@ def _element_constructor_(self, x):
 
         return self.element_class(self, x)
 
+    def monomial(self, arg):
+        r"""
+        Return the monomial with the given exponent.
+        """
+        return self.element_class(self, {arg: self.base_ring().one()})
+
     def __reduce__(self):
         """
         Used in pickling.
@@ -591,6 +599,9 @@ def __init__(self, R):
         if not R.base_ring().is_integral_domain():
             raise ValueError("base ring must be an integral domain")
         LaurentPolynomialRing_generic.__init__(self, R)
+        from sage.modules.free_module import FreeModule
+        from sage.rings.integer_ring import IntegerRing
+        self._indices = FreeModule(IntegerRing(), R.ngens())
 
     Element = LazyImport('sage.rings.polynomial.laurent_polynomial_mpair', 'LaurentPolynomial_mpair')
 
@@ -605,7 +616,7 @@ def _repr_(self):
         """
         return "Multivariate Laurent Polynomial Ring in %s over %s" % (", ".join(self._R.variable_names()), self._R.base_ring())
 
-    def monomial(self, *args):
+    def monomial(self, *exponents):
         r"""
         Return the monomial whose exponents are given in argument.
 
@@ -629,14 +640,27 @@ def monomial(self, *args):
             sage: L.monomial(1, 2, 3)                                                   # needs sage.modules
             Traceback (most recent call last):
             ...
-            TypeError: tuple key must have same length as ngens
-        """
-        if len(args) != self.ngens():
-            raise TypeError("tuple key must have same length as ngens")
+            TypeError: tuple key (1, 2, 3) must have same length as ngens (= 2)
+
+        We also allow to specify the exponents in a single tuple::
+
+            sage: L.monomial((-1, 2))                                                   # needs sage.modules
+            x0^-1*x1^2
 
+            sage: L.monomial((-1, 2, 3))                                                # needs sage.modules
+            Traceback (most recent call last):
+            ...
+            TypeError: tuple key (-1, 2, 3) must have same length as ngens (= 2)
+        """
         from sage.rings.polynomial.polydict import ETuple
-        m = ETuple(args, int(self.ngens()))
-        return self.element_class(self, self.polynomial_ring().one(), m)
+        if len(exponents) == 1 and isinstance((e := exponents[0]), (tuple, ETuple)):
+            exponents = e
+
+        if len(exponents) != self.ngens():
+            raise TypeError(f"tuple key {exponents} must have same length as ngens (= {self.ngens()})")
+
+        m = ETuple(exponents, int(self.ngens()))
+        return self.element_class(self, self.polynomial_ring().base_ring().one(), m)
 
     def _element_constructor_(self, x, mon=None):
         """

src/sage/rings/polynomial/laurent_polynomial_ring_base.py

@@ -42,6 +42,8 @@ class LaurentPolynomialRing_generic(CommutativeRing, Parent):
         sage: R.<x1,x2> = LaurentPolynomialRing(QQ)
         sage: R.category()
         Join of Category of unique factorization domains
+            and Category of algebras with basis
+                over (number fields and quotient fields and metric spaces)
             and Category of commutative algebras
                 over (number fields and quotient fields and metric spaces)
             and Category of infinite sets

src/sage/rings/polynomial/multi_polynomial_ring_base.pxd

@@ -4,6 +4,7 @@ from sage.structure.parent cimport Parent
 cdef class MPolynomialRing_base(CommutativeRing):
     cdef object _ngens
     cdef object _term_order
+    cdef public object _indices
     cdef public object _has_singular
     cdef public object _magma_gens
     cdef public dict _magma_cache

src/sage/rings/polynomial/multi_polynomial_ring_base.pyx

@@ -99,6 +99,8 @@ cdef class MPolynomialRing_base(CommutativeRing):
         else:
             category = polynomial_default_category(base_ring.category(), n)
         Ring.__init__(self, base_ring, names, category=category)
+        from sage.combinat.integer_vector import IntegerVectors
+        self._indices = IntegerVectors(self._ngens)
 
     def is_integral_domain(self, proof=True):
         """

src/sage/rings/polynomial/polynomial_ring.py

@@ -256,15 +256,25 @@ def __init__(self, base_ring, name=None, sparse=False, implementation=None,
 
             sage: category(ZZ['x'])
             Join of Category of unique factorization domains
+             and Category of algebras with basis over
+              (Dedekind domains and euclidean domains
+               and noetherian rings and infinite enumerated sets
+               and metric spaces)
              and Category of commutative algebras over
               (Dedekind domains and euclidean domains
                and noetherian rings and infinite enumerated sets
                and metric spaces)
              and Category of infinite sets
+
             sage: category(GF(7)['x'])
             Join of Category of euclidean domains
-             and Category of commutative algebras over
-              (finite enumerated fields and subquotients of monoids and quotients of semigroups) and Category of infinite sets
+             and Category of algebras with basis over
+              (finite enumerated fields and subquotients of monoids
+               and quotients of semigroups)
+            and Category of commutative algebras over
+              (finite enumerated fields and subquotients of monoids
+               and quotients of semigroups)
+            and Category of infinite sets
 
         TESTS:
 
@@ -314,6 +324,8 @@ def __init__(self, base_ring, name=None, sparse=False, implementation=None,
         self.__cyclopoly_cache = {}
         self._has_singular = False
         Ring.__init__(self, base_ring, names=name, normalize=True, category=category)
+        from sage.rings.semirings.non_negative_integer_semiring import NonNegativeIntegerSemiring
+        self._indices = NonNegativeIntegerSemiring()
         self._populate_coercion_lists_(convert_method_name='_polynomial_')
 
     def __reduce__(self):

src/sage/rings/polynomial/polynomial_ring_constructor.py

@@ -916,23 +916,30 @@ def polynomial_default_category(base_ring_category, n_variables):
     EXAMPLES::
 
         sage: from sage.rings.polynomial.polynomial_ring_constructor import polynomial_default_category
-        sage: polynomial_default_category(Rings(),1) is Algebras(Rings()).Infinite()
+        sage: polynomial_default_category(Rings(), 1)
+        Category of infinite algebras with basis over rings
+        sage: polynomial_default_category(Rings().Commutative(), 1)
+        Category of infinite commutative algebras with basis
+            over commutative rings
+        sage: polynomial_default_category(Fields(), 1)
+        Join of Category of euclidean domains
+            and Category of algebras with basis over fields
+            and Category of commutative algebras over fields
+            and Category of infinite sets
+        sage: polynomial_default_category(Fields(), 2)
+        Join of Category of unique factorization domains
+            and Category of algebras with basis over fields
+            and Category of commutative algebras over fields
+            and Category of infinite sets
+
+        sage: QQ['t'].category() is EuclideanDomains() & CommutativeAlgebras(QQ.category()).WithBasis().Infinite()
         True
-        sage: polynomial_default_category(Rings().Commutative(),1) is Algebras(Rings().Commutative()).Commutative().Infinite()
+        sage: QQ['s','t'].category() is UniqueFactorizationDomains() & CommutativeAlgebras(QQ.category()).WithBasis().Infinite()
         True
-        sage: polynomial_default_category(Fields(),1) is EuclideanDomains() & Algebras(Fields()).Infinite()
-        True
-        sage: polynomial_default_category(Fields(),2) is UniqueFactorizationDomains() & CommutativeAlgebras(Fields()).Infinite()
-        True
-
-        sage: QQ['t'].category() is EuclideanDomains() & CommutativeAlgebras(QQ.category()).Infinite()
-        True
-        sage: QQ['s','t'].category() is UniqueFactorizationDomains() & CommutativeAlgebras(QQ.category()).Infinite()
-        True
-        sage: QQ['s']['t'].category() is UniqueFactorizationDomains() & CommutativeAlgebras(QQ['s'].category()).Infinite()
+        sage: QQ['s']['t'].category() is UniqueFactorizationDomains() & CommutativeAlgebras(QQ['s'].category()).WithBasis().Infinite()
         True
     """
-    category = Algebras(base_ring_category)
+    category = Algebras(base_ring_category).WithBasis()
 
     if n_variables:
         # here we assume the base ring to be nonzero
@@ -1034,4 +1041,4 @@ def BooleanPolynomialRing_constructor(n=None, names=None, order='lex'):
 
 ############################################################################
 # END (Factory function for making polynomial rings)
-############################################################################
+############################################################################

src/sage/rings/ring.pyx

@@ -155,6 +155,7 @@ cdef class Ring(ParentWithGens):
           Running the test suite of self.an_element()
           running ._test_category() . . . pass
           running ._test_eq() . . . pass
+          running ._test_monomial_coefficients() . . . pass
           running ._test_new() . . . pass
           running ._test_nonzero_equal() . . . pass
           running ._test_not_implemented_methods() . . . pass
@@ -184,20 +185,29 @@ cdef class Ring(ParentWithGens):
     Test against another bug fixed in :issue:`9944`::
 
         sage: QQ['x'].category()
-        Join of Category of euclidean domains and Category of commutative algebras over
-         (number fields and quotient fields and metric spaces) and Category of infinite sets
+        Join of Category of euclidean domains
+            and Category of algebras with basis
+                over (number fields and quotient fields and metric spaces)
+            and Category of commutative algebras
+                over (number fields and quotient fields and metric spaces)
+            and Category of infinite sets
         sage: QQ['x','y'].category()
         Join of Category of unique factorization domains
+            and Category of algebras with basis
+                over (number fields and quotient fields and metric spaces)
             and Category of commutative algebras
                 over (number fields and quotient fields and metric spaces)
             and Category of infinite sets
         sage: PolynomialRing(MatrixSpace(QQ, 2),'x').category()                         # needs sage.modules
-        Category of infinite algebras over (finite dimensional algebras with basis over
-         (number fields and quotient fields and metric spaces) and infinite sets)
+        Category of infinite algebras with basis
+            over (finite dimensional algebras with basis
+                    over (number fields and quotient fields and metric spaces)
+                  and infinite sets)
         sage: PolynomialRing(SteenrodAlgebra(2),'x').category()                         # needs sage.combinat sage.modules
-        Category of infinite algebras over (super Hopf algebras with basis
-         over Finite Field of size 2 and supercocommutative super coalgebras
-         over Finite Field of size 2)
+        Category of infinite algebras with basis
+            over (super Hopf algebras with basis over Finite Field of size 2
+                  and supercocommutative super coalgebras
+                      over Finite Field of size 2)
 
     TESTS::