Rings¶
This module provides the abstract base class Ring
from which
all rings in Sage (used to) derive, as well as a selection of more
specific base classes.
Warning
Those classes, except maybe for the lowest ones like Ring
,
CommutativeRing
, Algebra
and CommutativeAlgebra
,
are being progressively deprecated in favor of the corresponding
categories. which are more flexible, in particular with respect to multiple
inheritance.
The class inheritance hierarchy is:
Subclasses of PrincipalIdealDomain
are
Some aspects of this structure may seem strange, but this is an unfortunate
consequence of the fact that Cython classes do not support multiple
inheritance. Hence, for instance, Field
cannot be a subclass of both
NoetherianRing
and PrincipalIdealDomain
, although all fields
are Noetherian PIDs.
(A distinct but equally awkward issue is that sometimes we may not know in
advance whether or not a ring belongs in one of these classes; e.g. some
orders in number fields are Dedekind domains, but others are not, and we still
want to offer a unified interface, so orders are never instances of the
DedekindDomain
class.)
AUTHORS:
 David Harvey (20061016): changed
CommutativeAlgebra
to derive fromCommutativeRing
instead of fromAlgebra
.  David Loeffler (20090709): documentation fixes, added to reference manual.
 Simon King (20110329): Proper use of the category framework for rings.
 Simon King (20110520): Modify multiplication and _ideal_class_ to support ideals of noncommutative rings.

class
sage.rings.ring.
Algebra
¶ Bases:
sage.rings.ring.Ring
Generic algebra

characteristic
()¶ Return the characteristic of this algebra, which is the same as the characteristic of its base ring.
See objects with the
base_ring
attribute for additional examples. Here are some examples that explicitly use theAlgebra
class.EXAMPLES:
sage: A = Algebra(ZZ); A <sage.rings.ring.Algebra object at ...> sage: A.characteristic() 0 sage: A = Algebra(GF(7^3, 'a')) sage: A.characteristic() 7

has_standard_involution
()¶ Return
True
if the algebra has a standard involution andFalse
otherwise. This algorithm follows Algorithm 2.10 from John Voight’s Identifying the Matrix Ring. Currently the only type of algebra this will work for is a quaternion algebra. Though this function seems redundant, once algebras have more functionality, in particular have a method to construct a basis, this algorithm will have more general purpose.EXAMPLES:
sage: B = QuaternionAlgebra(2) sage: B.has_standard_involution() True sage: R.<x> = PolynomialRing(QQ) sage: K.<u> = NumberField(x**2  2) sage: A = QuaternionAlgebra(K,2,5) sage: A.has_standard_involution() True sage: L.<a,b> = FreeAlgebra(QQ,2) sage: L.has_standard_involution() Traceback (most recent call last): ... NotImplementedError: has_standard_involution is not implemented for this algebra


class
sage.rings.ring.
CommutativeAlgebra
¶ Bases:
sage.rings.ring.CommutativeRing
Generic commutative algebra

is_commutative
()¶ Return
True
since this algebra is commutative.EXAMPLES:
Any commutative ring is a commutative algebra over itself:
sage: A = sage.rings.ring.CommutativeAlgebra sage: A(ZZ).is_commutative() True sage: A(QQ).is_commutative() True
Trying to create a commutative algebra over a noncommutative ring will result in a
TypeError
.


class
sage.rings.ring.
CommutativeRing
¶ Bases:
sage.rings.ring.Ring
Generic commutative ring.

derivation
(arg=None, twist=None)¶ Return the twisted or untwisted derivation over this ring specified by
arg
.Note
A twisted derivation with respect to \(\theta\) (or a \(\theta\)derivation for short) is an additive map \(d\) satisfying the following axiom for all \(x, y\) in the domain:
\[d(xy) = \theta(x) d(y) + d(x) y.\]INPUT:
arg
– (optional) a generator or a list of coefficients that defines the derivationtwist
– (optional) the twisting homomorphism
EXAMPLES:
sage: R.<x,y,z> = QQ[] sage: R.derivation() d/dx
In that case,
arg
could be a generator:sage: R.derivation(y) d/dy
or a list of coefficients:
sage: R.derivation([1,2,3]) d/dx + 2*d/dy + 3*d/dz
It is not possible to define derivations with respect to a polynomial which is not a variable:
sage: R.derivation(x^2) Traceback (most recent call last): ... ValueError: unable to create the derivation
Here is an example with twisted derivations:
sage: R.<x,y,z> = QQ[] sage: theta = R.hom([x^2, y^2, z^2]) sage: f = R.derivation(twist=theta); f 0 sage: f.parent() Module of twisted derivations over Multivariate Polynomial Ring in x, y, z over Rational Field (twisting morphism: x > x^2, y > y^2, z > z^2)
Specifying a scalar, the returned twisted derivation is the corresponding multiple of \(\theta  id\):
sage: R.derivation(1, twist=theta) [x > x^2, y > y^2, z > z^2]  id sage: R.derivation(x, twist=theta) x*([x > x^2, y > y^2, z > z^2]  id)

derivation_module
(codomain=None, twist=None)¶ Returns the module of derivations over this ring.
INPUT:
codomain
– an algebra over this ring or a ring homomorphism whose domain is this ring orNone
(default:None
); if it is a morphism, the codomain of derivations will be the codomain of the morphism viewed as an algebra overself
through the given morphism; ifNone
, the codomain will be this ringtwist
– a morphism from this ring tocodomain
orNone
(default:None
); ifNone
, the coercion map from this ring tocodomain
will be used
Note
A twisted derivation with respect to \(\theta\) (or a \(\theta\)derivation for short) is an additive map \(d\) satisfying the following axiom for all \(x, y\) in the domain:
\[d(xy) = \theta(x) d(y) + d(x) y.\]EXAMPLES:
sage: R.<x,y,z> = QQ[] sage: M = R.derivation_module(); M Module of derivations over Multivariate Polynomial Ring in x, y, z over Rational Field sage: M.gens() (d/dx, d/dy, d/dz)
We can specify a different codomain:
sage: K = R.fraction_field() sage: M = R.derivation_module(K); M Module of derivations from Multivariate Polynomial Ring in x, y, z over Rational Field to Fraction Field of Multivariate Polynomial Ring in x, y, z over Rational Field sage: M.gen() / x 1/x*d/dx
Here is an example with a noncanonical defining morphism:
sage: ev = R.hom([QQ(0), QQ(1), QQ(2)]) sage: ev Ring morphism: From: Multivariate Polynomial Ring in x, y, z over Rational Field To: Rational Field Defn: x > 0 y > 1 z > 2 sage: M = R.derivation_module(ev) sage: M Module of derivations from Multivariate Polynomial Ring in x, y, z over Rational Field to Rational Field
Elements in \(M\) acts as derivations at \((0,1,2)\):
sage: Dx = M.gen(0); Dx d/dx sage: Dy = M.gen(1); Dy d/dy sage: Dz = M.gen(2); Dz d/dz sage: f = x^2 + y^2 + z^2 sage: Dx(f) # = 2*x evaluated at (0,1,2) 0 sage: Dy(f) # = 2*y evaluated at (0,1,2) 2 sage: Dz(f) # = 2*z evaluated at (0,1,2) 4
An example with a twisting homomorphism:
sage: theta = R.hom([x^2, y^2, z^2]) sage: M = R.derivation_module(twist=theta); M Module of twisted derivations over Multivariate Polynomial Ring in x, y, z over Rational Field (twisting morphism: x > x^2, y > y^2, z > z^2)
See also

extension
(poly, name=None, names=None, **kwds)¶ Algebraically extends self by taking the quotient
self[x] / (f(x))
.INPUT:
poly
– A polynomial whose coefficients are coercible intoself
name
– (optional) name for the root of \(f\)
Note
Using this method on an algebraically complete field does not return this field; the construction
self[x] / (f(x))
is done anyway.EXAMPLES:
sage: R = QQ['x'] sage: y = polygen(R) sage: R.extension(y^2  5, 'a') Univariate Quotient Polynomial Ring in a over Univariate Polynomial Ring in x over Rational Field with modulus a^2  5
sage: P.<x> = PolynomialRing(GF(5)) sage: F.<a> = GF(5).extension(x^2  2) sage: P.<t> = F[] sage: R.<b> = F.extension(t^2  a); R Univariate Quotient Polynomial Ring in b over Finite Field in a of size 5^2 with modulus b^2 + 4*a

fraction_field
()¶ Return the fraction field of
self
.EXAMPLES:
sage: R = Integers(389)['x,y'] sage: Frac(R) Fraction Field of Multivariate Polynomial Ring in x, y over Ring of integers modulo 389 sage: R.fraction_field() Fraction Field of Multivariate Polynomial Ring in x, y over Ring of integers modulo 389

frobenius_endomorphism
(n=1)¶ INPUT:
n
– a nonnegative integer (default: 1)
OUTPUT:
The \(n\)th power of the absolute arithmetic Frobenius endomorphism on this finite field.
EXAMPLES:
sage: K.<u> = PowerSeriesRing(GF(5)) sage: Frob = K.frobenius_endomorphism(); Frob Frobenius endomorphism x > x^5 of Power Series Ring in u over Finite Field of size 5 sage: Frob(u) u^5
We can specify a power:
sage: f = K.frobenius_endomorphism(2); f Frobenius endomorphism x > x^(5^2) of Power Series Ring in u over Finite Field of size 5 sage: f(1+u) 1 + u^25

ideal_monoid
()¶ Return the monoid of ideals of this ring.
EXAMPLES:
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

is_commutative
()¶ Return
True
, since this ring is commutative.EXAMPLES:
sage: QQ.is_commutative() True sage: ZpCA(7).is_commutative() True sage: A = QuaternionAlgebra(QQ, 1, 3, names=('i','j','k')); A Quaternion Algebra (1, 3) with base ring Rational Field sage: A.is_commutative() False

krull_dimension
()¶ Return the Krull dimension of this commutative ring.
The Krull dimension is the length of the longest ascending chain of prime ideals.


class
sage.rings.ring.
DedekindDomain
¶ Bases:
sage.rings.ring.IntegralDomain
Generic Dedekind domain class.
A Dedekind domain is a Noetherian integral domain of Krull dimension one that is integrally closed in its field of fractions.
This class is deprecated, and not actually used anywhere in the Sage code base. If you think you need it, please create a category
DedekindDomains
, move the code of this class there, and use it instead.
integral_closure
()¶ Return
self
since Dedekind domains are integrally closed.EXAMPLES:
sage: K = NumberField(x^2 + 1, 's') sage: OK = K.ring_of_integers() sage: OK.integral_closure() Gaussian Integers in Number Field in s with defining polynomial x^2 + 1 sage: OK.integral_closure() == OK True sage: QQ.integral_closure() == QQ True

is_integrally_closed
()¶ Return
True
since Dedekind domains are integrally closed.EXAMPLES:
The following are examples of Dedekind domains (Noetherian integral domains of Krull dimension one that are integrally closed over its field of fractions).
sage: ZZ.is_integrally_closed() True sage: K = NumberField(x^2 + 1, 's') sage: OK = K.ring_of_integers() sage: OK.is_integrally_closed() True
These, however, are not Dedekind domains:
sage: QQ.is_integrally_closed() True sage: S = ZZ[sqrt(5)]; S.is_integrally_closed() False sage: T.<x,y> = PolynomialRing(QQ,2); T Multivariate Polynomial Ring in x, y over Rational Field sage: T.is_integral_domain() True

is_noetherian
()¶ Return
True
since Dedekind domains are Noetherian.EXAMPLES:
The integers, \(\ZZ\), and rings of integers of number fields are Dedekind domains:
sage: ZZ.is_noetherian() True sage: K = NumberField(x^2 + 1, 's') sage: OK = K.ring_of_integers() sage: OK.is_noetherian() True sage: QQ.is_noetherian() True

krull_dimension
()¶ Return 1 since Dedekind domains have Krull dimension 1.
EXAMPLES:
The following are examples of Dedekind domains (Noetherian integral domains of Krull dimension one that are integrally closed over its field of fractions):
sage: ZZ.krull_dimension() 1 sage: K = NumberField(x^2 + 1, 's') sage: OK = K.ring_of_integers() sage: OK.krull_dimension() 1
The following are not Dedekind domains but have a
krull_dimension
function:sage: QQ.krull_dimension() 0 sage: T.<x,y> = PolynomialRing(QQ,2); T Multivariate Polynomial Ring in x, y over Rational Field sage: T.krull_dimension() 2 sage: U.<x,y,z> = PolynomialRing(ZZ,3); U Multivariate Polynomial Ring in x, y, z over Integer Ring sage: U.krull_dimension() 4 sage: K.<i> = QuadraticField(1) sage: R = K.order(2*i); R Order in Number Field in i with defining polynomial x^2 + 1 with i = 1*I sage: R.is_maximal() False sage: R.krull_dimension() 1


class
sage.rings.ring.
EuclideanDomain
¶ Bases:
sage.rings.ring.PrincipalIdealDomain
Generic Euclidean domain class.
This class is deprecated. Please use the
EuclideanDomains
category instead.
parameter
()¶ Return an element of degree 1.
EXAMPLES:
sage: R.<x>=QQ[] sage: R.parameter() x


class
sage.rings.ring.
Field
¶ Bases:
sage.rings.ring.PrincipalIdealDomain
Generic field

algebraic_closure
()¶ Return the algebraic closure of
self
.Note
This is only implemented for certain classes of field.
EXAMPLES:
sage: K = PolynomialRing(QQ,'x').fraction_field(); K Fraction Field of Univariate Polynomial Ring in x over Rational Field sage: K.algebraic_closure() Traceback (most recent call last): ... NotImplementedError: Algebraic closures of general fields not implemented.

divides
(x, y, coerce=True)¶ Return
True
ifx
dividesy
in this field (usuallyTrue
in a field!). Ifcoerce
isTrue
(the default), first coercex
andy
intoself
.EXAMPLES:
sage: QQ.divides(2, 3/4) True sage: QQ.divides(0, 5) False

fraction_field
()¶ Return the fraction field of
self
.EXAMPLES:
Since fields are their own field of fractions, we simply get the original field in return:
sage: QQ.fraction_field() Rational Field sage: RR.fraction_field() Real Field with 53 bits of precision sage: CC.fraction_field() Complex Field with 53 bits of precision sage: F = NumberField(x^2 + 1, 'i') sage: F.fraction_field() Number Field in i with defining polynomial x^2 + 1

ideal
(*gens, **kwds)¶ Return the ideal generated by gens.
EXAMPLES:
sage: QQ.ideal(2) Principal ideal (1) of Rational Field sage: QQ.ideal(0) Principal ideal (0) of Rational Field

integral_closure
()¶ Return this field, since fields are integrally closed in their fraction field.
EXAMPLES:
sage: QQ.integral_closure() Rational Field sage: Frac(ZZ['x,y']).integral_closure() Fraction Field of Multivariate Polynomial Ring in x, y over Integer Ring

is_field
(proof=True)¶ Return
True
since this is a field.EXAMPLES:
sage: Frac(ZZ['x,y']).is_field() True

is_integrally_closed
()¶ Return
True
since fields are trivially integrally closed in their fraction field (since they are their own fraction field).EXAMPLES:
sage: Frac(ZZ['x,y']).is_integrally_closed() True

is_noetherian
()¶ Return
True
since fields are Noetherian rings.EXAMPLES:
sage: QQ.is_noetherian() True

krull_dimension
()¶ Return the Krull dimension of this field, which is 0.
EXAMPLES:
sage: QQ.krull_dimension() 0 sage: Frac(QQ['x,y']).krull_dimension() 0

prime_subfield
()¶ Return the prime subfield of
self
.EXAMPLES:
sage: k = GF(9, 'a') sage: k.prime_subfield() Finite Field of size 3


class
sage.rings.ring.
IntegralDomain
¶ Bases:
sage.rings.ring.CommutativeRing
Generic integral domain class.
This class is deprecated. Please use the
sage.categories.integral_domains.IntegralDomains
category instead.
is_field
(proof=True)¶ Return
True
if this ring is a field.EXAMPLES:
sage: GF(7).is_field() True
The following examples have their own
is_field
implementations:sage: ZZ.is_field(); QQ.is_field() False True sage: R.<x> = PolynomialRing(QQ); R.is_field() False

is_integral_domain
(proof=True)¶ Return
True
, since this ring is an integral domain.(This is a naive implementation for objects with type
IntegralDomain
)EXAMPLES:
sage: ZZ.is_integral_domain() True sage: QQ.is_integral_domain() True sage: ZZ['x'].is_integral_domain() True sage: R = ZZ.quotient(ZZ.ideal(10)); R.is_integral_domain() False

is_integrally_closed
()¶ Return
True
if this ring is integrally closed in its field of fractions; otherwise returnFalse
.When no algorithm is implemented for this, then this function raises a
NotImplementedError
.Note that
is_integrally_closed
has a naive implementation in fields. For every field \(F\), \(F\) is its own field of fractions, hence every element of \(F\) is integral over \(F\).EXAMPLES:
sage: ZZ.is_integrally_closed() True sage: QQ.is_integrally_closed() True sage: QQbar.is_integrally_closed() True sage: GF(5).is_integrally_closed() True sage: Z5 = Integers(5); Z5 Ring of integers modulo 5 sage: Z5.is_integrally_closed() Traceback (most recent call last): ... AttributeError: 'IntegerModRing_generic_with_category' object has no attribute 'is_integrally_closed'


class
sage.rings.ring.
NoetherianRing
¶ Bases:
sage.rings.ring.CommutativeRing
Generic Noetherian ring class.
A Noetherian ring is a commutative ring in which every ideal is finitely generated.
This class is deprecated, and not actually used anywhere in the Sage code base. If you think you need it, please create a category
NoetherianRings
, move the code of this class there, and use it instead.
is_noetherian
()¶ Return
True
since this ring is Noetherian.EXAMPLES:
sage: ZZ.is_noetherian() True sage: QQ.is_noetherian() True sage: R.<x> = PolynomialRing(QQ) sage: R.is_noetherian() True


class
sage.rings.ring.
PrincipalIdealDomain
¶ Bases:
sage.rings.ring.IntegralDomain
Generic principal ideal domain.
This class is deprecated. Please use the
PrincipalIdealDomains
category instead.
class_group
()¶ Return the trivial group, since the class group of a PID is trivial.
EXAMPLES:
sage: QQ.class_group() Trivial Abelian group

content
(x, y, coerce=True)¶ Return the content of \(x\) and \(y\), i.e. the unique element \(c\) of
self
such that \(x/c\) and \(y/c\) are coprime and integral.EXAMPLES:
sage: QQ.content(ZZ(42), ZZ(48)); type(QQ.content(ZZ(42), ZZ(48))) 6 <type 'sage.rings.rational.Rational'> sage: QQ.content(1/2, 1/3) 1/6 sage: factor(1/2); factor(1/3); factor(1/6) 2^1 3^1 2^1 * 3^1 sage: a = (2*3)/(7*11); b = (13*17)/(19*23) sage: factor(a); factor(b); factor(QQ.content(a,b)) 2 * 3 * 7^1 * 11^1 13 * 17 * 19^1 * 23^1 7^1 * 11^1 * 19^1 * 23^1
Note the changes to the second entry:
sage: c = (2*3)/(7*11); d = (13*17)/(7*19*23) sage: factor(c); factor(d); factor(QQ.content(c,d)) 2 * 3 * 7^1 * 11^1 7^1 * 13 * 17 * 19^1 * 23^1 7^1 * 11^1 * 19^1 * 23^1 sage: e = (2*3)/(7*11); f = (13*17)/(7^3*19*23) sage: factor(e); factor(f); factor(QQ.content(e,f)) 2 * 3 * 7^1 * 11^1 7^3 * 13 * 17 * 19^1 * 23^1 7^3 * 11^1 * 19^1 * 23^1

gcd
(x, y, coerce=True)¶ Return the greatest common divisor of
x
andy
, as elements ofself
.EXAMPLES:
The integers are a principal ideal domain and hence a GCD domain:
sage: ZZ.gcd(42, 48) 6 sage: 42.factor(); 48.factor() 2 * 3 * 7 2^4 * 3 sage: ZZ.gcd(2^4*7^2*11, 2^3*11*13) 88 sage: 88.factor() 2^3 * 11
In a field, any nonzero element is a GCD of any nonempty set of nonzero elements. In previous versions, Sage used to return 1 in the case of the rational field. However, since trac ticket #10771, the rational field is considered as the fraction field of the integer ring. For the fraction field of an integral domain that provides both GCD and LCM, it is possible to pick a GCD that is compatible with the GCD of the base ring:
sage: QQ.gcd(ZZ(42), ZZ(48)); type(QQ.gcd(ZZ(42), ZZ(48))) 6 <type 'sage.rings.rational.Rational'> sage: QQ.gcd(1/2, 1/3) 1/6
Polynomial rings over fields are GCD domains as well. Here is a simple example over the ring of polynomials over the rationals as well as over an extension ring. Note that
gcd
requires x and y to be coercible:sage: R.<x> = PolynomialRing(QQ) sage: S.<a> = NumberField(x^2  2, 'a') sage: f = (x  a)*(x + a); g = (x  a)*(x^2  2) sage: print(f); print(g) x^2  2 x^3  a*x^2  2*x + 2*a sage: f in R True sage: g in R False sage: R.gcd(f,g) Traceback (most recent call last): ... TypeError: Unable to coerce 2*a to a rational sage: R.base_extend(S).gcd(f,g) x^2  2 sage: R.base_extend(S).gcd(f, (x  a)*(x^2  3)) x  a

is_noetherian
()¶ Every principal ideal domain is noetherian, so we return
True
.EXAMPLES:
sage: Zp(5).is_noetherian() True


class
sage.rings.ring.
Ring
¶ Bases:
sage.structure.parent_gens.ParentWithGens
Generic ring class.

base_extend
(R)¶ EXAMPLES:
sage: QQ.base_extend(GF(7)) Traceback (most recent call last): ... TypeError: no base extension defined sage: ZZ.base_extend(GF(7)) Finite Field of size 7

category
()¶ Return the category to which this ring belongs.
Note
This method exists because sometimes a ring is its own base ring. During initialisation of a ring \(R\), it may be checked whether the base ring (hence, the ring itself) is a ring. Hence, it is necessary that
R.category()
tells thatR
is a ring, even before its category is properly initialised.EXAMPLES:
sage: FreeAlgebra(QQ, 3, 'x').category() # todo: use a ring which is not an algebra! Category of algebras with basis over Rational Field
Since a quotient of the integers is its own base ring, and during initialisation of a ring it is tested whether the base ring belongs to the category of rings, the following is an indirect test that the
category()
method of rings returns the category of rings even before the initialisation was successful:sage: I = Integers(15) sage: I.base_ring() is I True sage: I.category() Join of Category of finite commutative rings and Category of subquotients of monoids and Category of quotients of semigroups and Category of finite enumerated sets

epsilon
()¶ Return the precision error of elements in this ring.
EXAMPLES:
sage: RDF.epsilon() 2.220446049250313e16 sage: ComplexField(53).epsilon() 2.22044604925031e16 sage: RealField(10).epsilon() 0.0020
For exact rings, zero is returned:
sage: ZZ.epsilon() 0
This also works over derived rings:
sage: RR['x'].epsilon() 2.22044604925031e16 sage: QQ['x'].epsilon() 0
For the symbolic ring, there is no reasonable answer:
sage: SR.epsilon() Traceback (most recent call last): ... NotImplementedError

ideal
(*args, **kwds)¶ Return the ideal defined by
x
, i.e., generated byx
.INPUT:
*x
– list or tuple of generators (or several input arguments)coerce
– bool (default:True
); this must be a keyword argument. Only set it toFalse
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 ofIdeal_generic
orIdeal_nc
. Further named arguments (such as
side
in the case of noncommutative rings) are forwarded to the ideal class.
EXAMPLES:
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
Here is an example over a noncommutative ring:
sage: A = SteenrodAlgebra(2) sage: A.ideal(A.1,A.2^2) Twosided Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis sage: A.ideal(A.1,A.2^2,side='left') Left Ideal (Sq(2), Sq(2,2)) of mod 2 Steenrod algebra, milnor basis

ideal_monoid
()¶ Return the monoid of ideals of this ring.
EXAMPLES:
sage: F.<x,y,z> = FreeAlgebra(ZZ, 3) sage: I = F*[x*y+y*z,x^2+x*yy*xy^2]*F sage: Q = sage.rings.ring.Ring.quotient(F,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*yy*xy^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)

is_commutative
()¶ Return
True
if this ring is commutative.EXAMPLES:
sage: QQ.is_commutative() True sage: QQ['x,y,z'].is_commutative() True sage: Q.<i,j,k> = QuaternionAlgebra(QQ, 1,1) sage: Q.is_commutative() False

is_exact
()¶ Return
True
if elements of this ring are represented exactly, i.e., there is no precision loss when doing arithmetic.Note
This defaults to
True
, so even if it does returnTrue
you have no guarantee (unless the ring has properly overloaded this).EXAMPLES:
sage: QQ.is_exact() # indirect doctest True sage: ZZ.is_exact() True sage: Qp(7).is_exact() False sage: Zp(7, type='cappedabs').is_exact() False

is_field
(proof=True)¶ Return
True
if this ring is a field.INPUT:
proof
– (default:True
) Determines what to do in unknown cases
ALGORITHM:
If the parameter
proof
is set toTrue
, the returned value is correct but the method might throw an error. Otherwise, if it is set toFalse
, the method returns True if it can establish that self is a field and False otherwise.EXAMPLES:
sage: QQ.is_field() True sage: GF(9,'a').is_field() True sage: ZZ.is_field() False sage: QQ['x'].is_field() False sage: Frac(QQ['x']).is_field() True
This illustrates the use of the
proof
parameter:sage: R.<a,b> = QQ[] sage: S.<x,y> = R.quo((b^3)) sage: S.is_field(proof = True) Traceback (most recent call last): ... NotImplementedError sage: S.is_field(proof = False) False

is_integral_domain
(proof=True)¶ Return
True
if this ring is an integral domain.INPUT:
proof
– (default:True
) Determines what to do in unknown cases
ALGORITHM:
If the parameter
proof
is set toTrue
, the returned value is correct but the method might throw an error. Otherwise, if it is set toFalse
, the method returnsTrue
if it can establish that self is an integral domain andFalse
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() True sage: Qp(7).is_integral_domain() True sage: R.<a,b> = QQ[] sage: S.<x,y> = R.quo((b^3)) sage: S.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)) sage: S.is_integral_domain(proof = True) Traceback (most recent call last): ... NotImplementedError sage: S.is_integral_domain(proof = False) False

is_noetherian
()¶ Return
True
if this ring is Noetherian.EXAMPLES:
sage: QQ.is_noetherian() True sage: ZZ.is_noetherian() True

is_prime_field
()¶ 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() False sage: ZZ.is_prime_field() False sage: QQ['x'].is_prime_field() False sage: Qp(19).is_prime_field() False

is_ring
()¶ Return
True
sinceself
is a ring.EXAMPLES:
sage: QQ.is_ring() True

is_subring
(other)¶ Return
True
if the canonical map fromself
toother
is injective.Raises a
NotImplementedError
if not known.EXAMPLES:
sage: ZZ.is_subring(QQ) True sage: ZZ.is_subring(GF(19)) False

one
()¶ Return the one element of this ring (cached), if it exists.
EXAMPLES:
sage: ZZ.one() 1 sage: QQ.one() 1 sage: QQ['x'].one() 1
The result is cached:
sage: ZZ.one() is ZZ.one() True

order
()¶ The number of elements of
self
.EXAMPLES:
sage: GF(19).order() 19 sage: QQ.order() +Infinity

principal_ideal
(gen, coerce=True)¶ 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

quo
(I, names=None)¶ Create the quotient of \(R\) by the ideal \(I\). This is a synonym for
quotient()
EXAMPLES:
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

quotient
(I, names=None)¶ Create the quotient of this ring by a twosided ideal
I
.INPUT:
I
– a twosided ideal of this ring, \(R\).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).
EXAMPLES:
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: 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

quotient_ring
(I, names=None)¶ Return the quotient of self by the ideal \(I\) of
self
. (Synonym forself.quotient(I)
.)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.)
OUTPUT:
R/I
– the quotient ring of \(R\) by the ideal \(I\)
EXAMPLES:
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: 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

random_element
(bound=2)¶ Return a random integer coerced into this ring, where the integer is chosen uniformly from the interval
[bound,bound]
.INPUT:
bound
– integer (default: 2)
ALGORITHM:
Uses Python’s randint.

unit_ideal
()¶ Return the unit ideal of this ring.
EXAMPLES:
sage: Zp(7).unit_ideal() Principal ideal (1 + O(7^20)) of 7adic Ring with capped relative precision 20

zero
()¶ Return the zero element of this ring (cached).
EXAMPLES:
sage: ZZ.zero() 0 sage: QQ.zero() 0 sage: QQ['x'].zero() 0
The result is cached:
sage: ZZ.zero() is ZZ.zero() True

zero_ideal
()¶ 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
The result is cached:
sage: ZZ.zero_ideal() is ZZ.zero_ideal() True

zeta
(n=2, all=False)¶ Return a primitive
n
th root of unity inself
if there is one, or raise aValueError
otherwise.INPUT:
n
– positive integerall
– bool (default: False)  whether to return a list of all primitive \(n\)th roots of unity. If True, raise aValueError
ifself
is not an integral domain.
OUTPUT:
Element of
self
of finite orderEXAMPLES:
sage: QQ.zeta() 1 sage: QQ.zeta(1) 1 sage: CyclotomicField(6).zeta(6) zeta6 sage: CyclotomicField(3).zeta(3) zeta3 sage: CyclotomicField(3).zeta(3).multiplicative_order() 3 sage: a = GF(7).zeta(); a 3 sage: a.multiplicative_order() 6 sage: a = GF(49,'z').zeta(); a z sage: a.multiplicative_order() 48 sage: a = GF(49,'z').zeta(2); a 6 sage: a.multiplicative_order() 2 sage: QQ.zeta(3) Traceback (most recent call last): ... ValueError: no nth root of unity in rational field sage: Zp(7, prec=8).zeta() 3 + 4*7 + 6*7^2 + 3*7^3 + 2*7^5 + 6*7^6 + 2*7^7 + O(7^8)

zeta_order
()¶ Return the order of the distinguished root of unity in
self
.EXAMPLES:
sage: CyclotomicField(19).zeta_order() 38 sage: GF(19).zeta_order() 18 sage: GF(5^3,'a').zeta_order() 124 sage: Zp(7, prec=8).zeta_order() 6


sage.rings.ring.
is_Ring
(x)¶ Return
True
ifx
is a ring.EXAMPLES:
sage: from sage.rings.ring import is_Ring sage: is_Ring(ZZ) True sage: MS = MatrixSpace(QQ,2) sage: is_Ring(MS) True