Rings

class sage.categories.rings.Rings(base_category)[source]

Bases: CategoryWithAxiom_singleton

The category of rings.

Associative rings with unit, not necessarily commutative

EXAMPLES:

sage: Rings()
Category of rings
sage: sorted(Rings().super_categories(), key=str)
[Category of rngs, Category of semirings]

sage: sorted(Rings().axioms())
['AdditiveAssociative', 'AdditiveCommutative', 'AdditiveInverse',
 'AdditiveUnital', 'Associative', 'Distributive', 'Unital']

sage: Rings() is (CommutativeAdditiveGroups() & Monoids()).Distributive()
True
sage: Rings() is Rngs().Unital()
True
sage: Rings() is Semirings().AdditiveInverse()
True

>>> from sage.all import *
>>> Rings()
Category of rings
>>> sorted(Rings().super_categories(), key=str)
[Category of rngs, Category of semirings]

>>> sorted(Rings().axioms())
['AdditiveAssociative', 'AdditiveCommutative', 'AdditiveInverse',
 'AdditiveUnital', 'Associative', 'Distributive', 'Unital']

>>> Rings() is (CommutativeAdditiveGroups() & Monoids()).Distributive()
True
>>> Rings() is Rngs().Unital()
True
>>> Rings() is Semirings().AdditiveInverse()
True

Todo

(see Issue #sage_trac/wiki/CategoriesRoadMap)

  • Make Rings() into a subcategory or alias of Algebras(ZZ);

  • A parent P in the category Rings() should automatically be in the category Algebras(P).

Commutative[source]

alias of CommutativeRings

Division[source]

alias of DivisionRings

class ElementMethods[source]

Bases: object

inverse_of_unit()[source]

Return the inverse of this element if it is a unit.

OUTPUT: an element in the same ring as this element

EXAMPLES:

sage: R.<x> = ZZ[]
sage: S = R.quo(x^2 + x + 1)                                            # needs sage.libs.pari
sage: S(1).inverse_of_unit()                                            # needs sage.libs.pari
1

>>> from sage.all import *
>>> R = ZZ['x']; (x,) = R._first_ngens(1)
>>> S = R.quo(x**Integer(2) + x + Integer(1))                                            # needs sage.libs.pari
>>> S(Integer(1)).inverse_of_unit()                                            # needs sage.libs.pari
1

This method fails when the element is not a unit:

sage: 2.inverse_of_unit()
Traceback (most recent call last):
...
ArithmeticError: inverse does not exist

>>> from sage.all import *
>>> Integer(2).inverse_of_unit()
Traceback (most recent call last):
...
ArithmeticError: inverse does not exist

The inverse returned is in the same ring as this element:

sage: a = -1
sage: a.parent()
Integer Ring
sage: a.inverse_of_unit().parent()
Integer Ring

>>> from sage.all import *
>>> a = -Integer(1)
>>> a.parent()
Integer Ring
>>> a.inverse_of_unit().parent()
Integer Ring

Note that this is often not the case when computing inverses in other ways:

sage: (~a).parent()
Rational Field
sage: (1/a).parent()
Rational Field

>>> from sage.all import *
>>> (~a).parent()
Rational Field
>>> (Integer(1)/a).parent()
Rational Field
is_unit()[source]

Return whether this element is a unit in the ring.

Note

This is a generic implementation for (non-commutative) rings which only works for the one element, its additive inverse, and the zero element. Most rings should provide a more specialized implementation.

EXAMPLES:

sage: # needs sage.modules
sage: MS = MatrixSpace(ZZ, 2)
sage: MS.one().is_unit()
True
sage: MS.zero().is_unit()
False
sage: MS([1,2,3,4]).is_unit()
False

>>> from sage.all import *
>>> # needs sage.modules
>>> MS = MatrixSpace(ZZ, Integer(2))
>>> MS.one().is_unit()
True
>>> MS.zero().is_unit()
False
>>> MS([Integer(1),Integer(2),Integer(3),Integer(4)]).is_unit()
False
class MorphismMethods[source]

Bases: object

extend_to_fraction_field()[source]

Return the extension of this morphism to fraction fields of the domain and the codomain.

EXAMPLES:

sage: S.<x> = QQ[]
sage: f = S.hom([x + 1]); f
Ring endomorphism of Univariate Polynomial Ring in x over Rational Field
    Defn: x |--> x + 1

sage: g = f.extend_to_fraction_field(); g                               # needs sage.libs.singular
Ring endomorphism of Fraction Field of Univariate Polynomial Ring in x
 over Rational Field
    Defn: x |--> x + 1
sage: g(x)                                                              # needs sage.libs.singular
x + 1
sage: g(1/x)                                                            # needs sage.libs.singular
1/(x + 1)

>>> from sage.all import *
>>> S = QQ['x']; (x,) = S._first_ngens(1)
>>> f = S.hom([x + Integer(1)]); f
Ring endomorphism of Univariate Polynomial Ring in x over Rational Field
    Defn: x |--> x + 1

>>> g = f.extend_to_fraction_field(); g                               # needs sage.libs.singular
Ring endomorphism of Fraction Field of Univariate Polynomial Ring in x
 over Rational Field
    Defn: x |--> x + 1
>>> g(x)                                                              # needs sage.libs.singular
x + 1
>>> g(Integer(1)/x)                                                            # needs sage.libs.singular
1/(x + 1)

If this morphism is not injective, it does not extend to the fraction field and an error is raised:

sage: f = GF(5).coerce_map_from(ZZ)
sage: f.extend_to_fraction_field()
Traceback (most recent call last):
...
ValueError: the morphism is not injective

>>> from sage.all import *
>>> f = GF(Integer(5)).coerce_map_from(ZZ)
>>> f.extend_to_fraction_field()
Traceback (most recent call last):
...
ValueError: the morphism is not injective
is_injective()[source]

Return whether or not this morphism is injective.

EXAMPLES:

sage: # needs sage.libs.singular
sage: R.<x,y> = QQ[]
sage: R.hom([x, y^2], R).is_injective()
True
sage: R.hom([x, x^2], R).is_injective()
False
sage: S.<u,v> = R.quotient(x^3*y)
sage: R.hom([v, u], S).is_injective()
False
sage: S.hom([-u, v], S).is_injective()
True
sage: S.cover().is_injective()
False

>>> from sage.all import *
>>> # needs sage.libs.singular
>>> R = QQ['x, y']; (x, y,) = R._first_ngens(2)
>>> R.hom([x, y**Integer(2)], R).is_injective()
True
>>> R.hom([x, x**Integer(2)], R).is_injective()
False
>>> S = R.quotient(x**Integer(3)*y, names=('u', 'v',)); (u, v,) = S._first_ngens(2)
>>> R.hom([v, u], S).is_injective()
False
>>> S.hom([-u, v], S).is_injective()
True
>>> S.cover().is_injective()
False

If the domain is a field, the homomorphism is injective:

sage: K.<x> = FunctionField(QQ)
sage: L.<y> = FunctionField(QQ)
sage: f = K.hom([y]); f
Function Field morphism:
  From: Rational function field in x over Rational Field
  To:   Rational function field in y over Rational Field
  Defn: x |--> y
sage: f.is_injective()
True

>>> from sage.all import *
>>> K = FunctionField(QQ, names=('x',)); (x,) = K._first_ngens(1)
>>> L = FunctionField(QQ, names=('y',)); (y,) = L._first_ngens(1)
>>> f = K.hom([y]); f
Function Field morphism:
  From: Rational function field in x over Rational Field
  To:   Rational function field in y over Rational Field
  Defn: x |--> y
>>> f.is_injective()
True

Unless the codomain is the zero ring:

sage: codomain = Integers(1)
sage: f = QQ.hom([Zmod(1)(0)], check=False)
sage: f.is_injective()
False

>>> from sage.all import *
>>> codomain = Integers(Integer(1))
>>> f = QQ.hom([Zmod(Integer(1))(Integer(0))], check=False)
>>> f.is_injective()
False

Homomorphism from rings of characteristic zero to rings of positive characteristic can not be injective:

sage: R.<x> = ZZ[]
sage: f = R.hom([GF(3)(1)]); f
Ring morphism:
  From: Univariate Polynomial Ring in x over Integer Ring
  To:   Finite Field of size 3
  Defn: x |--> 1
sage: f.is_injective()
False

>>> from sage.all import *
>>> R = ZZ['x']; (x,) = R._first_ngens(1)
>>> f = R.hom([GF(Integer(3))(Integer(1))]); f
Ring morphism:
  From: Univariate Polynomial Ring in x over Integer Ring
  To:   Finite Field of size 3
  Defn: x |--> 1
>>> f.is_injective()
False

A morphism whose domain is an order in a number field is injective if the codomain has characteristic zero:

sage: K.<x> = FunctionField(QQ)
sage: f = ZZ.hom(K); f
Composite map:
  From: Integer Ring
  To:   Rational function field in x over Rational Field
  Defn:   Conversion via FractionFieldElement_1poly_field map:
          From: Integer Ring
          To:   Fraction Field of Univariate Polynomial Ring in x
                over Rational Field
        then
          Isomorphism:
          From: Fraction Field of Univariate Polynomial Ring in x
                over Rational Field
          To:   Rational function field in x over Rational Field
sage: f.is_injective()
True

>>> from sage.all import *
>>> K = FunctionField(QQ, names=('x',)); (x,) = K._first_ngens(1)
>>> f = ZZ.hom(K); f
Composite map:
  From: Integer Ring
  To:   Rational function field in x over Rational Field
  Defn:   Conversion via FractionFieldElement_1poly_field map:
          From: Integer Ring
          To:   Fraction Field of Univariate Polynomial Ring in x
                over Rational Field
        then
          Isomorphism:
          From: Fraction Field of Univariate Polynomial Ring in x
                over Rational Field
          To:   Rational function field in x over Rational Field
>>> f.is_injective()
True

A coercion to the fraction field is injective:

sage: R = ZpFM(3)                                                       # needs sage.rings.padics
sage: R.fraction_field().coerce_map_from(R).is_injective()
True

>>> from sage.all import *
>>> R = ZpFM(Integer(3))                                                       # needs sage.rings.padics
>>> R.fraction_field().coerce_map_from(R).is_injective()
True
NoZeroDivisors[source]

alias of Domains

class ParentMethods[source]

Bases: object

bracket(x, y)[source]

Return the Lie bracket \([x, y] = x y - y x\) of \(x\) and \(y\).

INPUT:

  • x, y – elements of self

EXAMPLES:

sage: # needs sage.combinat sage.modules
sage: F = AlgebrasWithBasis(QQ).example()
sage: F
An example of an algebra with basis:
 the free algebra on the generators ('a', 'b', 'c') over Rational Field
sage: a, b, c = F.algebra_generators()
sage: F.bracket(a, b)
B[word: ab] - B[word: ba]

>>> from sage.all import *
>>> # needs sage.combinat sage.modules
>>> F = AlgebrasWithBasis(QQ).example()
>>> F
An example of an algebra with basis:
 the free algebra on the generators ('a', 'b', 'c') over Rational Field
>>> a, b, c = F.algebra_generators()
>>> F.bracket(a, b)
B[word: ab] - B[word: ba]

This measures the default of commutation between \(x\) and \(y\). \(F\) endowed with the bracket operation is a Lie algebra; in particular, it satisfies Jacobi’s identity:

sage: (F.bracket(F.bracket(a,b), c) + F.bracket(F.bracket(b,c), a)      # needs sage.combinat sage.modules
....:  + F.bracket(F.bracket(c,a), b))
0

>>> from sage.all import *
>>> (F.bracket(F.bracket(a,b), c) + F.bracket(F.bracket(b,c), a)      # needs sage.combinat sage.modules
...  + F.bracket(F.bracket(c,a), b))
0
characteristic()[source]

Return the characteristic of this ring.

EXAMPLES:

sage: QQ.characteristic()
0
sage: GF(19).characteristic()
19
sage: Integers(8).characteristic()
8
sage: Zp(5).characteristic()                                            # needs sage.rings.padics
0

>>> from sage.all import *
>>> QQ.characteristic()
0
>>> GF(Integer(19)).characteristic()
19
>>> Integers(Integer(8)).characteristic()
8
>>> Zp(Integer(5)).characteristic()                                            # needs sage.rings.padics
0
free_module(base=None, basis=None, map=True)[source]

Return a free module \(V\) over the specified subring together with maps to and from \(V\).

The default implementation only supports the case that the base ring is the ring itself.

INPUT:

  • base – a subring \(R\) so that this ring is isomorphic to a finite-rank free \(R\)-module \(V\)

  • basis – (optional) a basis for this ring over the base

  • map – boolean (default: True); whether to return \(R\)-linear maps to and from \(V\)

OUTPUT: a finite-rank free \(R\)-module \(V\)

  • An \(R\)-module isomorphism from \(V\) to this ring (only included if map is True)

  • An \(R\)-module isomorphism from this ring to \(V\) (only included if map is True)

EXAMPLES:

sage: # needs sage.modules
sage: R.<x> = QQ[[]]
sage: V, from_V, to_V = R.free_module(R)
sage: v = to_V(1 + x); v
(1 + x)
sage: from_V(v)
1 + x
sage: W, from_W, to_W = R.free_module(R, basis=(1 - x))
sage: W is V
True
sage: w = to_W(1 + x); w
(1 - x^2)
sage: from_W(w)
1 + x + O(x^20)

>>> from sage.all import *
>>> # needs sage.modules
>>> R = QQ[['x']]; (x,) = R._first_ngens(1)
>>> V, from_V, to_V = R.free_module(R)
>>> v = to_V(Integer(1) + x); v
(1 + x)
>>> from_V(v)
1 + x
>>> W, from_W, to_W = R.free_module(R, basis=(Integer(1) - x))
>>> W is V
True
>>> w = to_W(Integer(1) + x); w
(1 - x^2)
>>> from_W(w)
1 + x + O(x^20)
ideal(*args, **kwds)[source]

Create an ideal of this ring.

INPUT:

  • an element or a list/tuple/sequence of elements, the generators

  • coerce – boolean (default: True); whether to first coerce the elements into this ring. This must be a keyword argument. Only set it to False if you are certain that each generator is already in the ring.

  • ideal_class – callable (default: self._ideal_class_()); this must be a keyword argument. A constructor for ideals, taking the ring as the first argument and then the generators. Usually a subclass of Ideal_generic or Ideal_nc.

  • Further named arguments (such as side in the case of non-commutative rings) are forwarded to the ideal class.

The keyword side can be one of 'twosided', 'left', 'right'. It determines whether the resulting ideal is twosided, a left ideal or a right ideal.

EXAMPLES:

Matrix rings:

sage: # needs sage.modules
sage: MS = MatrixSpace(QQ, 2, 2)
sage: MS.ideal(2)
Twosided Ideal
(
  [2 0]
  [0 2]
)
 of Full MatrixSpace of 2 by 2 dense matrices over Rational Field
sage: MS.ideal([MS.0, MS.1], side='right')
Right Ideal
(
  [1 0]
  [0 0],

  [0 1]
  [0 0]
)
 of Full MatrixSpace of 2 by 2 dense matrices over Rational Field

>>> from sage.all import *
>>> # needs sage.modules
>>> MS = MatrixSpace(QQ, Integer(2), Integer(2))
>>> MS.ideal(Integer(2))
Twosided Ideal
(
  [2 0]
  [0 2]
)
 of Full MatrixSpace of 2 by 2 dense matrices over Rational Field
>>> MS.ideal([MS.gen(0), MS.gen(1)], side='right')
Right Ideal
(
  [1 0]
  [0 0],
<BLANKLINE>
  [0 1]
  [0 0]
)
 of Full MatrixSpace of 2 by 2 dense matrices over Rational Field

Polynomial rings:

sage: R.<x,y> = QQ[]
sage: R.ideal(x,y)
Ideal (x, y) of Multivariate Polynomial Ring in x, y over Rational Field
sage: R.ideal(x+y^2)
Ideal (y^2 + x) of Multivariate Polynomial Ring in x, y over Rational Field
sage: R.ideal( [x^3,y^3+x^3] )
Ideal (x^3, x^3 + y^3) of Multivariate Polynomial Ring in x, y over Rational Field

>>> from sage.all import *
>>> R = QQ['x, y']; (x, y,) = R._first_ngens(2)
>>> R.ideal(x,y)
Ideal (x, y) of Multivariate Polynomial Ring in x, y over Rational Field
>>> R.ideal(x+y**Integer(2))
Ideal (y^2 + x) of Multivariate Polynomial Ring in x, y over Rational Field
>>> R.ideal( [x**Integer(3),y**Integer(3)+x**Integer(3)] )
Ideal (x^3, x^3 + y^3) of Multivariate Polynomial Ring in x, y over Rational Field

Non-commutative rings:

sage: A = SteenrodAlgebra(2)                                                # needs sage.combinat sage.modules
sage: A.ideal(A.1, A.2^2)                                                   # needs sage.combinat sage.modules
Twosided Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis
sage: A.ideal(A.1, A.2^2, side='left')                                      # needs sage.combinat sage.modules
Left Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis

>>> from sage.all import *
>>> A = SteenrodAlgebra(Integer(2))                                                # needs sage.combinat sage.modules
>>> A.ideal(A.gen(1), A.gen(2)**Integer(2))                                                   # needs sage.combinat sage.modules
Twosided Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis
>>> A.ideal(A.gen(1), A.gen(2)**Integer(2), side='left')                                      # needs sage.combinat sage.modules
Left Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis
ideal_monoid()[source]

The monoid of the ideals of this ring.

EXAMPLES:

sage: # needs sage.modules
sage: MS = MatrixSpace(QQ, 2, 2)
sage: isinstance(MS, Ring)
False
sage: MS in Rings()
True
sage: MS.ideal_monoid()
Monoid of ideals of Full MatrixSpace of 2 by 2 dense matrices
over Rational Field

>>> from sage.all import *
>>> # needs sage.modules
>>> MS = MatrixSpace(QQ, Integer(2), Integer(2))
>>> isinstance(MS, Ring)
False
>>> MS in Rings()
True
>>> MS.ideal_monoid()
Monoid of ideals of Full MatrixSpace of 2 by 2 dense matrices
over Rational Field

Note that the monoid is cached:

sage: MS.ideal_monoid() is MS.ideal_monoid()                            # needs sage.modules
True

>>> from sage.all import *
>>> MS.ideal_monoid() is MS.ideal_monoid()                            # needs sage.modules
True

More examples:

sage: # needs sage.combinat sage.modules
sage: F.<x,y,z> = FreeAlgebra(ZZ, 3)
sage: I = F * [x*y + y*z, x^2 + x*y - y*x - y^2] * F
sage: Q = F.quotient(I)
sage: Q.ideal_monoid()
Monoid of ideals of Quotient of Free Algebra on 3 generators (x, y, z)
 over Integer Ring by the ideal (x*y + y*z, x^2 + x*y - y*x - y^2)
sage: F.<x,y,z> = FreeAlgebra(ZZ, implementation='letterplace')
sage: I = F * [x*y + y*z, x^2 + x*y - y*x - y^2] * F
sage: Q = F.quo(I)
sage: Q.ideal_monoid()
Monoid of ideals of Quotient of Free Associative Unital Algebra
 on 3 generators (x, y, z) over Integer Ring
 by the ideal (x*y + y*z, x*x + x*y - y*x - y*y)

sage: ZZ.ideal_monoid()
Monoid of ideals of Integer Ring
sage: R.<x> = QQ[]; R.ideal_monoid()
Monoid of ideals of Univariate Polynomial Ring in x over Rational Field

>>> from sage.all import *
>>> # needs sage.combinat sage.modules
>>> F = FreeAlgebra(ZZ, Integer(3), names=('x', 'y', 'z',)); (x, y, z,) = F._first_ngens(3)
>>> I = F * [x*y + y*z, x**Integer(2) + x*y - y*x - y**Integer(2)] * F
>>> Q = F.quotient(I)
>>> Q.ideal_monoid()
Monoid of ideals of Quotient of Free Algebra on 3 generators (x, y, z)
 over Integer Ring by the ideal (x*y + y*z, x^2 + x*y - y*x - y^2)
>>> F = FreeAlgebra(ZZ, implementation='letterplace', names=('x', 'y', 'z',)); (x, y, z,) = F._first_ngens(3)
>>> I = F * [x*y + y*z, x**Integer(2) + x*y - y*x - y**Integer(2)] * F
>>> Q = F.quo(I)
>>> Q.ideal_monoid()
Monoid of ideals of Quotient of Free Associative Unital Algebra
 on 3 generators (x, y, z) over Integer Ring
 by the ideal (x*y + y*z, x*x + x*y - y*x - y*y)

>>> ZZ.ideal_monoid()
Monoid of ideals of Integer Ring
>>> R = QQ['x']; (x,) = R._first_ngens(1); R.ideal_monoid()
Monoid of ideals of Univariate Polynomial Ring in x over Rational Field
is_commutative()[source]

Return whether the ring is commutative.

The answer is True only if the category is a sub-category of CommutativeRings.

It is recommended to use instead R in Rings().Commutative().

EXAMPLES:

sage: Q.<i,j,k> = QuaternionAlgebra(QQ, -1, -1)                             # needs sage.combinat sage.modules
sage: Q.is_commutative()                                                    # needs sage.combinat sage.modules
False

>>> from sage.all import *
>>> Q = QuaternionAlgebra(QQ, -Integer(1), -Integer(1), names=('i', 'j', 'k',)); (i, j, k,) = Q._first_ngens(3)# needs sage.combinat sage.modules
>>> Q.is_commutative()                                                    # needs sage.combinat sage.modules
False
is_integral_domain(proof=True)[source]

Return True if this ring is an integral domain.

INPUT:

  • proof – boolean (default: True); determine what to do in unknown cases

ALGORITHM:

If the parameter proof is set to True, the returned value is correct but the method might throw an error. Otherwise, if it is set to False, the method returns True if it can establish that self is an integral domain and False otherwise.

EXAMPLES:

sage: QQ.is_integral_domain()
True
sage: ZZ.is_integral_domain()
True
sage: ZZ['x,y,z'].is_integral_domain()
True
sage: Integers(8).is_integral_domain()
False
sage: Zp(7).is_integral_domain()                                            # needs sage.rings.padics
True
sage: Qp(7).is_integral_domain()                                            # needs sage.rings.padics
True
sage: R.<a,b> = QQ[]
sage: S.<x,y> = R.quo((b^3))                                                # needs sage.libs.singular
sage: S.is_integral_domain()                                                # needs sage.libs.singular
False
sage: R = ZZ.quotient(ZZ.ideal(10)); R.is_integral_domain()
False

>>> from sage.all import *
>>> QQ.is_integral_domain()
True
>>> ZZ.is_integral_domain()
True
>>> ZZ['x,y,z'].is_integral_domain()
True
>>> Integers(Integer(8)).is_integral_domain()
False
>>> Zp(Integer(7)).is_integral_domain()                                            # needs sage.rings.padics
True
>>> Qp(Integer(7)).is_integral_domain()                                            # needs sage.rings.padics
True
>>> R = QQ['a, b']; (a, b,) = R._first_ngens(2)
>>> S = R.quo((b**Integer(3)), names=('x', 'y',)); (x, y,) = S._first_ngens(2)# needs sage.libs.singular
>>> S.is_integral_domain()                                                # needs sage.libs.singular
False
>>> R = ZZ.quotient(ZZ.ideal(Integer(10))); R.is_integral_domain()
False

This illustrates the use of the proof parameter:

sage: R.<a,b> = ZZ[]
sage: S.<x,y> = R.quo((b^3))                                                # needs sage.libs.singular
sage: S.is_integral_domain(proof=True)                                      # needs sage.libs.singular
Traceback (most recent call last):
...
NotImplementedError
sage: S.is_integral_domain(proof=False)                                     # needs sage.libs.singular
False

>>> from sage.all import *
>>> R = ZZ['a, b']; (a, b,) = R._first_ngens(2)
>>> S = R.quo((b**Integer(3)), names=('x', 'y',)); (x, y,) = S._first_ngens(2)# needs sage.libs.singular
>>> S.is_integral_domain(proof=True)                                      # needs sage.libs.singular
Traceback (most recent call last):
...
NotImplementedError
>>> S.is_integral_domain(proof=False)                                     # needs sage.libs.singular
False
is_noetherian()[source]

Return True if this ring is Noetherian.

EXAMPLES:

sage: QQ.is_noetherian()
True
sage: ZZ.is_noetherian()
True

>>> from sage.all import *
>>> QQ.is_noetherian()
True
>>> ZZ.is_noetherian()
True
is_prime_field()[source]

Return True if this ring is one of the prime fields \(\QQ\) or \(\GF{p}\).

EXAMPLES:

sage: QQ.is_prime_field()
True
sage: GF(3).is_prime_field()
True
sage: GF(9, 'a').is_prime_field()                                           # needs sage.rings.finite_rings
False
sage: ZZ.is_prime_field()
False
sage: QQ['x'].is_prime_field()
False
sage: Qp(19).is_prime_field()                                               # needs sage.rings.padics
False

>>> from sage.all import *
>>> QQ.is_prime_field()
True
>>> GF(Integer(3)).is_prime_field()
True
>>> GF(Integer(9), 'a').is_prime_field()                                           # needs sage.rings.finite_rings
False
>>> ZZ.is_prime_field()
False
>>> QQ['x'].is_prime_field()
False
>>> Qp(Integer(19)).is_prime_field()                                               # needs sage.rings.padics
False
is_ring()[source]

Return True, since this in an object of the category of rings.

EXAMPLES:

sage: Parent(QQ,category=Rings()).is_ring()
True

>>> from sage.all import *
>>> Parent(QQ,category=Rings()).is_ring()
True
is_subring(other)[source]

Return True if the canonical map from self to other is injective.

This raises a NotImplementedError if not known.

EXAMPLES:

sage: ZZ.is_subring(QQ)
True
sage: ZZ.is_subring(GF(19))
False

>>> from sage.all import *
>>> ZZ.is_subring(QQ)
True
>>> ZZ.is_subring(GF(Integer(19)))
False
is_zero()[source]

Return True if this is the zero ring.

EXAMPLES:

sage: Integers(1).is_zero()
True
sage: Integers(2).is_zero()
False
sage: QQ.is_zero()
False
sage: R.<x> = ZZ[]
sage: R.quo(1).is_zero()
True
sage: R.<x> = GF(101)[]
sage: R.quo(77).is_zero()
True
sage: R.quo(x^2 + 1).is_zero()                                          # needs sage.libs.pari
False

>>> from sage.all import *
>>> Integers(Integer(1)).is_zero()
True
>>> Integers(Integer(2)).is_zero()
False
>>> QQ.is_zero()
False
>>> R = ZZ['x']; (x,) = R._first_ngens(1)
>>> R.quo(Integer(1)).is_zero()
True
>>> R = GF(Integer(101))['x']; (x,) = R._first_ngens(1)
>>> R.quo(Integer(77)).is_zero()
True
>>> R.quo(x**Integer(2) + Integer(1)).is_zero()                                          # needs sage.libs.pari
False
principal_ideal(gen, coerce=True)[source]

Return the principal ideal generated by gen.

EXAMPLES:

sage: R.<x,y> = ZZ[]
sage: R.principal_ideal(x+2*y)
Ideal (x + 2*y) of Multivariate Polynomial Ring in x, y over Integer Ring

>>> from sage.all import *
>>> R = ZZ['x, y']; (x, y,) = R._first_ngens(2)
>>> R.principal_ideal(x+Integer(2)*y)
Ideal (x + 2*y) of Multivariate Polynomial Ring in x, y over Integer Ring
quo(I, names=None, **kwds)[source]

Quotient of a ring by a two-sided ideal.

Note

This is a synonym for quotient().

EXAMPLES:

sage: MS = MatrixSpace(QQ, 2)                                           # needs sage.modules
sage: I = MS * MS.gens() * MS                                           # needs sage.modules

>>> from sage.all import *
>>> MS = MatrixSpace(QQ, Integer(2))                                           # needs sage.modules
>>> I = MS * MS.gens() * MS                                           # needs sage.modules

MS is not an instance of Ring.

However it is an instance of the parent class of the category of rings. The quotient method is inherited from there:

sage: isinstance(MS, sage.rings.ring.Ring)                              # needs sage.modules
False
sage: isinstance(MS, Rings().parent_class)                              # needs sage.modules
True
sage: MS.quo(I, names=['a','b','c','d'])                                # needs sage.modules
Quotient of Full MatrixSpace of 2 by 2 dense matrices
 over Rational Field by the ideal
(
  [1 0]
  [0 0],

  [0 1]
  [0 0],

  [0 0]
  [1 0],

  [0 0]
  [0 1]
)

>>> from sage.all import *
>>> isinstance(MS, sage.rings.ring.Ring)                              # needs sage.modules
False
>>> isinstance(MS, Rings().parent_class)                              # needs sage.modules
True
>>> MS.quo(I, names=['a','b','c','d'])                                # needs sage.modules
Quotient of Full MatrixSpace of 2 by 2 dense matrices
 over Rational Field by the ideal
(
  [1 0]
  [0 0],
<BLANKLINE>
  [0 1]
  [0 0],
<BLANKLINE>
  [0 0]
  [1 0],
<BLANKLINE>
  [0 0]
  [0 1]
)

A test with a subclass of Ring:

sage: # needs sage.libs.singular
sage: R.<x,y> = PolynomialRing(QQ, 2)
sage: S.<a,b> = R.quo((x^2, y))
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
sage: S.gens()
(a, 0)
sage: a == b
False

>>> from sage.all import *
>>> # needs sage.libs.singular
>>> R = PolynomialRing(QQ, Integer(2), names=('x', 'y',)); (x, y,) = R._first_ngens(2)
>>> S = R.quo((x**Integer(2), y), names=('a', 'b',)); (a, b,) = S._first_ngens(2)
>>> S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
>>> S.gens()
(a, 0)
>>> a == b
False
quotient(I, names=None, **kwds)[source]

Quotient of a ring by a two-sided ideal.

INPUT:

  • I – a twosided ideal of this ring

  • names – (optional) names of the generators of the quotient (if there are multiple generators, you can specify a single character string and the generators are named in sequence starting with 0).

  • further named arguments that may be passed to the quotient ring constructor.

EXAMPLES:

Usually, a ring inherits a method sage.rings.ring.Ring.quotient(). So, we need a bit of effort to make the following example work with the category framework:

sage: # needs sage.combinat sage.modules
sage: F.<x,y,z> = FreeAlgebra(QQ)
sage: from sage.rings.noncommutative_ideals import Ideal_nc
sage: from itertools import product
sage: class PowerIdeal(Ideal_nc):
....:  def __init__(self, R, n):
....:      self._power = n
....:      Ideal_nc.__init__(self, R, [R.prod(m)
....:                                  for m in product(R.gens(), repeat=n)])
....:  def reduce(self, x):
....:      R = self.ring()
....:      return add([c*R(m) for m, c in x
....:                  if len(m) < self._power], R(0))
sage: I = PowerIdeal(F, 3)
sage: Q = Rings().parent_class.quotient(F, I); Q
Quotient of Free Algebra on 3 generators (x, y, z) over Rational Field
 by the ideal (x^3, x^2*y, x^2*z, x*y*x, x*y^2, x*y*z, x*z*x,
               x*z*y, x*z^2, y*x^2, y*x*y, y*x*z, y^2*x, y^3,
               y^2*z, y*z*x, y*z*y, y*z^2, z*x^2, z*x*y, z*x*z,
               z*y*x, z*y^2, z*y*z, z^2*x, z^2*y, z^3)
sage: Q.0
xbar
sage: Q.1
ybar
sage: Q.2
zbar
sage: Q.0*Q.1
xbar*ybar
sage: Q.0*Q.1*Q.0
0

>>> from sage.all import *
>>> # needs sage.combinat sage.modules
>>> F = FreeAlgebra(QQ, names=('x', 'y', 'z',)); (x, y, z,) = F._first_ngens(3)
>>> from sage.rings.noncommutative_ideals import Ideal_nc
>>> from itertools import product
>>> class PowerIdeal(Ideal_nc):
...  def __init__(self, R, n):
...      self._power = n
...      Ideal_nc.__init__(self, R, [R.prod(m)
...                                  for m in product(R.gens(), repeat=n)])
...  def reduce(self, x):
...      R = self.ring()
...      return add([c*R(m) for m, c in x
...                  if len(m) < self._power], R(Integer(0)))
>>> I = PowerIdeal(F, Integer(3))
>>> Q = Rings().parent_class.quotient(F, I); Q
Quotient of Free Algebra on 3 generators (x, y, z) over Rational Field
 by the ideal (x^3, x^2*y, x^2*z, x*y*x, x*y^2, x*y*z, x*z*x,
               x*z*y, x*z^2, y*x^2, y*x*y, y*x*z, y^2*x, y^3,
               y^2*z, y*z*x, y*z*y, y*z^2, z*x^2, z*x*y, z*x*z,
               z*y*x, z*y^2, z*y*z, z^2*x, z^2*y, z^3)
>>> Q.gen(0)
xbar
>>> Q.gen(1)
ybar
>>> Q.gen(2)
zbar
>>> Q.gen(0)*Q.gen(1)
xbar*ybar
>>> Q.gen(0)*Q.gen(1)*Q.gen(0)
0

An example with polynomial rings:

sage: R.<x> = PolynomialRing(ZZ)
sage: I = R.ideal([4 + 3*x + x^2, 1 + x^2])
sage: S = R.quotient(I, 'a')
sage: S.gens()
(a,)

sage: # needs sage.libs.singular
sage: R.<x,y> = PolynomialRing(QQ, 2)
sage: S.<a,b> = R.quotient((x^2, y))
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
sage: S.gens()
(a, 0)
sage: a == b
False

>>> from sage.all import *
>>> R = PolynomialRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> I = R.ideal([Integer(4) + Integer(3)*x + x**Integer(2), Integer(1) + x**Integer(2)])
>>> S = R.quotient(I, 'a')
>>> S.gens()
(a,)

>>> # needs sage.libs.singular
>>> R = PolynomialRing(QQ, Integer(2), names=('x', 'y',)); (x, y,) = R._first_ngens(2)
>>> S = R.quotient((x**Integer(2), y), names=('a', 'b',)); (a, b,) = S._first_ngens(2)
>>> S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
>>> S.gens()
(a, 0)
>>> a == b
False
quotient_ring(I, names=None, **kwds)[source]

Quotient of a ring by a two-sided ideal.

Note

This is a synonym for quotient().

INPUT:

  • I – an ideal of \(R\)

  • names – (optional) names of the generators of the quotient. (If there are multiple generators, you can specify a single character string and the generators are named in sequence starting with 0.)

  • further named arguments that may be passed to the quotient ring constructor.

OUTPUT: R/I – the quotient ring of \(R\) by the ideal \(I\)

EXAMPLES:

sage: MS = MatrixSpace(QQ, 2)                                           # needs sage.modules
sage: I = MS * MS.gens() * MS                                           # needs sage.modules

>>> from sage.all import *
>>> MS = MatrixSpace(QQ, Integer(2))                                           # needs sage.modules
>>> I = MS * MS.gens() * MS                                           # needs sage.modules

MS is not an instance of Ring, but it is an instance of the parent class of the category of rings. The quotient method is inherited from there:

sage: isinstance(MS, sage.rings.ring.Ring)                              # needs sage.modules
False
sage: isinstance(MS, Rings().parent_class)                              # needs sage.modules
True
sage: MS.quotient_ring(I, names=['a','b','c','d'])                      # needs sage.modules
Quotient of Full MatrixSpace of 2 by 2 dense matrices
 over Rational Field by the ideal
(
  [1 0]
  [0 0],

  [0 1]
  [0 0],

  [0 0]
  [1 0],

  [0 0]
  [0 1]
)

>>> from sage.all import *
>>> isinstance(MS, sage.rings.ring.Ring)                              # needs sage.modules
False
>>> isinstance(MS, Rings().parent_class)                              # needs sage.modules
True
>>> MS.quotient_ring(I, names=['a','b','c','d'])                      # needs sage.modules
Quotient of Full MatrixSpace of 2 by 2 dense matrices
 over Rational Field by the ideal
(
  [1 0]
  [0 0],
<BLANKLINE>
  [0 1]
  [0 0],
<BLANKLINE>
  [0 0]
  [1 0],
<BLANKLINE>
  [0 0]
  [0 1]
)

A test with a subclass of Ring:

sage: R.<x> = PolynomialRing(ZZ)
sage: I = R.ideal([4 + 3*x + x^2, 1 + x^2])
sage: S = R.quotient_ring(I, 'a')
sage: S.gens()
(a,)

sage: # needs sage.libs.singular
sage: R.<x,y> = PolynomialRing(QQ,2)
sage: S.<a,b> = R.quotient_ring((x^2, y))
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
sage: S.gens()
(a, 0)
sage: a == b
False

>>> from sage.all import *
>>> R = PolynomialRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> I = R.ideal([Integer(4) + Integer(3)*x + x**Integer(2), Integer(1) + x**Integer(2)])
>>> S = R.quotient_ring(I, 'a')
>>> S.gens()
(a,)

>>> # needs sage.libs.singular
>>> R = PolynomialRing(QQ,Integer(2), names=('x', 'y',)); (x, y,) = R._first_ngens(2)
>>> S = R.quotient_ring((x**Integer(2), y), names=('a', 'b',)); (a, b,) = S._first_ngens(2)
>>> S
Quotient of Multivariate Polynomial Ring in x, y over Rational Field
 by the ideal (x^2, y)
>>> S.gens()
(a, 0)
>>> a == b
False
unit_ideal()[source]

Return the unit ideal of this ring.

EXAMPLES:

sage: Zp(7).unit_ideal()                                                    # needs sage.rings.padics
Principal ideal (1 + O(7^20)) of 7-adic Ring with capped relative precision 20

>>> from sage.all import *
>>> Zp(Integer(7)).unit_ideal()                                                    # needs sage.rings.padics
Principal ideal (1 + O(7^20)) of 7-adic Ring with capped relative precision 20
zero_ideal()[source]

Return the zero ideal of this ring (cached).

EXAMPLES:

sage: ZZ.zero_ideal()
Principal ideal (0) of Integer Ring
sage: QQ.zero_ideal()
Principal ideal (0) of Rational Field
sage: QQ['x'].zero_ideal()
Principal ideal (0) of Univariate Polynomial Ring in x over Rational Field

>>> from sage.all import *
>>> ZZ.zero_ideal()
Principal ideal (0) of Integer Ring
>>> QQ.zero_ideal()
Principal ideal (0) of Rational Field
>>> QQ['x'].zero_ideal()
Principal ideal (0) of Univariate Polynomial Ring in x over Rational Field

The result is cached:

sage: ZZ.zero_ideal() is ZZ.zero_ideal()
True

>>> from sage.all import *
>>> ZZ.zero_ideal() is ZZ.zero_ideal()
True
class SubcategoryMethods[source]

Bases: object

Division()[source]

Return the full subcategory of the division objects of self.

A ring satisfies the division axiom if all nonzero elements have multiplicative inverses.

EXAMPLES:

sage: Rings().Division()
Category of division rings
sage: Rings().Commutative().Division()
Category of fields

>>> from sage.all import *
>>> Rings().Division()
Category of division rings
>>> Rings().Commutative().Division()
Category of fields
NoZeroDivisors()[source]

Return the full subcategory of the objects of self having no nonzero zero divisors.

A zero divisor in a ring \(R\) is an element \(x \in R\) such that there exists a nonzero element \(y \in R\) such that \(x \cdot y = 0\) or \(y \cdot x = 0\) (see Wikipedia article Zero_divisor).

EXAMPLES:

sage: Rings().NoZeroDivisors()
Category of domains

>>> from sage.all import *
>>> Rings().NoZeroDivisors()
Category of domains