# Fields¶

class sage.categories.fields.Fields(base_category)

The category of (commutative) fields, i.e. commutative rings where all non-zero elements have multiplicative inverses

EXAMPLES:

sage: K = Fields()
sage: K
Category of fields
sage: Fields().super_categories()
[Category of euclidean domains, Category of division rings]

sage: K(IntegerRing())
Rational Field
sage: K(PolynomialRing(GF(3), 'x'))
Fraction Field of Univariate Polynomial Ring in x over
Finite Field of size 3
sage: K(RealField())
Real Field with 53 bits of precision


TESTS:

sage: TestSuite(Fields()).run()

class ElementMethods
euclidean_degree()

Return the degree of this element as an element of a euclidean domain.

In a field, this returns 0 for all but the zero element (for which it is undefined).

EXAMPLES:

sage: QQ.one().euclidean_degree()
0

gcd(other)

Greatest common divisor.

NOTE:

Since we are in a field and the greatest common divisor is only determined up to a unit, it is correct to either return zero or one. Note that fraction fields of unique factorization domains provide a more sophisticated gcd.

EXAMPLES:

sage: GF(5)(1).gcd(GF(5)(1))
1
sage: GF(5)(1).gcd(GF(5)(0))
1
sage: GF(5)(0).gcd(GF(5)(0))
0


For fields of characteristic zero (i.e., containing the integers as a sub-ring), evaluation in the integer ring is attempted. This is for backwards compatibility:

sage: gcd(6.0,8); gcd(6.0,8).parent()
2
Integer Ring


If this fails, we resort to the default we see above:

sage: gcd(6.0*CC.0,8*CC.0); gcd(6.0*CC.0,8*CC.0).parent()
1.00000000000000
Complex Field with 53 bits of precision


AUTHOR:

• Simon King (2011-02): Trac ticket #10771
is_unit()

Returns True if self has a multiplicative inverse.

EXAMPLES:

sage: QQ(2).is_unit()
True
sage: QQ(0).is_unit()
False

lcm(other)

Least common multiple.

NOTE:

Since we are in a field and the least common multiple is only determined up to a unit, it is correct to either return zero or one. Note that fraction fields of unique factorization domains provide a more sophisticated lcm.

EXAMPLES:

sage: GF(2)(1).lcm(GF(2)(0))
0
sage: GF(2)(1).lcm(GF(2)(1))
1


If the field contains the integer ring, it is first attempted to compute the gcd there:

sage: lcm(15.0,12.0); lcm(15.0,12.0).parent()
60
Integer Ring


If this fails, we resort to the default we see above:

sage: lcm(6.0*CC.0,8*CC.0); lcm(6.0*CC.0,8*CC.0).parent()
1.00000000000000
Complex Field with 53 bits of precision
sage: lcm(15.2,12.0)
1.00000000000000


AUTHOR:

• Simon King (2011-02): Trac ticket #10771
quo_rem(other)

Return the quotient with remainder of the division of this element by other.

INPUT:

• other – an element of the field

EXAMPLES:

sage: f,g = QQ(1), QQ(2)
sage: f.quo_rem(g)
(1/2, 0)

xgcd(other)

Compute the extended gcd of self and other.

INPUT:

• other – an element with the same parent as self

OUTPUT:

A tuple (r, s, t) of elements in the parent of self such that r = s * self + t * other. Since the computations are done over a field, r is zero if self and other are zero, and one otherwise.

AUTHORS:

EXAMPLES:

sage: (1/2).xgcd(2)
(1, 2, 0)
sage: (0/2).xgcd(2)
(1, 0, 1/2)
sage: (0/2).xgcd(0)
(0, 0, 0)

Fields.Finite

alias of FiniteFields

class Fields.ParentMethods
fraction_field()

Returns the fraction field of self, which is self.

EXAMPLES:

sage: QQ.fraction_field() is QQ
True

is_field(proof=True)

Returns True as self is a field.

EXAMPLES:

sage: QQ.is_field()
True
sage: Parent(QQ,category=Fields()).is_field()
True

is_integrally_closed()

Return True, as per IntegralDomain.is_integrally_closed(): for every field $$F$$, $$F$$ is its own field of fractions, hence every element of $$F$$ is integral over $$F$$.

EXAMPLES:

sage: QQ.is_integrally_closed()
True
sage: QQbar.is_integrally_closed()
True
sage: Z5 = GF(5); Z5
Finite Field of size 5
sage: Z5.is_integrally_closed()
True

is_perfect()

Return whether this field is perfect, i.e., its characteristic is $$p=0$$ or every element has a $$p$$-th root.

EXAMPLES:

sage: QQ.is_perfect()
True
sage: GF(2).is_perfect()
True
sage: FunctionField(GF(2), 'x').is_perfect()
False

Fields.extra_super_categories()

EXAMPLES:

sage: Fields().extra_super_categories()
[Category of euclidean domains]


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