\(p\)adic valuations on number fields and their subrings and completions¶
EXAMPLES:
sage: ZZ.valuation(2)
2adic valuation
sage: QQ.valuation(3)
3adic valuation
sage: CyclotomicField(5).valuation(5)
5adic valuation
sage: GaussianIntegers().valuation(7)
7adic valuation
sage: Zp(11).valuation()
11adic valuation
These valuations can then, e.g., be used to compute approximate factorizations in the completion of a ring:
sage: v = ZZ.valuation(2)
sage: R.<x> = ZZ[]
sage: f = x^5 + x^4 + x^3 + x^2 + x  1
sage: v.montes_factorization(f, required_precision=20)
(x + 676027) * (x^4 + 372550*x^3 + 464863*x^2 + 385052*x + 297869)
AUTHORS:
 Julian Rüth (20130316): initial version
REFERENCES:
The theory used here was originally developed in [Mac1936I] and [Mac1936II]. An overview can also be found in Chapter 4 of [Rüt2014].

class
sage.rings.padics.padic_valuation.
PadicValuationFactory
¶ Bases:
sage.structure.factory.UniqueFactory
Create a
prime
adic valuation onR
.INPUT:
R
– a subring of a number field or a subring of a local field in characteristic zeroprime
– a prime that does not split, a discrete (pseudo)valuation, a fractional ideal, orNone
(default:None
)
EXAMPLES:
For integers and rational numbers,
prime
is just a prime of the integers:sage: valuations.pAdicValuation(ZZ, 3) 3adic valuation sage: valuations.pAdicValuation(QQ, 3) 3adic valuation
prime
may beNone
for local rings:sage: valuations.pAdicValuation(Qp(2)) 2adic valuation sage: valuations.pAdicValuation(Zp(2)) 2adic valuation
But it must be specified in all other cases:
sage: valuations.pAdicValuation(ZZ) Traceback (most recent call last): ... ValueError: prime must be specified for this ring
It can sometimes be beneficial to define a number field extension as a quotient of a polynomial ring (since number field extensions always compute an absolute polynomial defining the extension which can be very costly):
sage: R.<x> = QQ[] sage: K.<a> = NumberField(x^2 + 1) sage: R.<x> = K[] sage: L.<b> = R.quo(x^2 + a) sage: valuations.pAdicValuation(L, 2) 2adic valuation
See also
NumberField_generic.valuation()
,Order.valuation()
,pAdicGeneric.valuation()
,RationalField.valuation()
,IntegerRing_class.valuation()
.
create_key_and_extra_args
(R, prime=None, approximants=None)¶ Create a unique key identifying the valuation of
R
with respect toprime
.EXAMPLES:
sage: QQ.valuation(2) # indirect doctest 2adic valuation

create_key_and_extra_args_for_number_field
(R, prime, approximants)¶ Create a unique key identifying the valuation of
R
with respect toprime
.EXAMPLES:
sage: GaussianIntegers().valuation(2) # indirect doctest 2adic valuation

create_key_and_extra_args_for_number_field_from_ideal
(R, I, prime)¶ Create a unique key identifying the valuation of
R
with respect toI
.Note
prime
, the original parameter that was passed tocreate_key_and_extra_args()
, is only used to provide more meaningful error messagesEXAMPLES:
sage: GaussianIntegers().valuation(GaussianIntegers().ideal(2)) # indirect doctest 2adic valuation

create_key_and_extra_args_for_number_field_from_valuation
(R, v, prime, approximants)¶ Create a unique key identifying the valuation of
R
with respect tov
.Note
prime
, the original parameter that was passed tocreate_key_and_extra_args()
, is only used to provide more meaningful error messagesEXAMPLES:
sage: GaussianIntegers().valuation(ZZ.valuation(2)) # indirect doctest 2adic valuation

create_key_for_integers
(R, prime)¶ Create a unique key identifying the valuation of
R
with respect toprime
.EXAMPLES:
sage: QQ.valuation(2) # indirect doctest 2adic valuation

create_key_for_local_ring
(R, prime)¶ Create a unique key identifying the valuation of
R
with respect toprime
.EXAMPLES:
sage: Qp(2).valuation() # indirect doctest 2adic valuation

create_object
(version, key, **extra_args)¶ Create a \(p\)adic valuation from
key
.EXAMPLES:
sage: ZZ.valuation(5) # indirect doctest 5adic valuation

class
sage.rings.padics.padic_valuation.
pAdicFromLimitValuation
(parent, approximant, G, approximants)¶ Bases:
sage.rings.valuation.mapped_valuation.FiniteExtensionFromLimitValuation
,sage.rings.padics.padic_valuation.pAdicValuation_base
A \(p\)adic valuation on a number field or a subring thereof, i.e., a valuation that extends the \(p\)adic valuation on the integers.
EXAMPLES:
sage: v = GaussianIntegers().valuation(3); v 3adic valuation

extensions
(ring)¶ Return the extensions of this valuation to
ring
.EXAMPLES:
sage: v = GaussianIntegers().valuation(3) sage: v.extensions(v.domain().fraction_field()) [3adic valuation]


class
sage.rings.padics.padic_valuation.
pAdicValuation_base
(parent, p)¶ Bases:
sage.rings.valuation.valuation.DiscreteValuation
Abstract base class for \(p\)adic valuations.
INPUT:
ring
– an integral domainp
– a rational prime over which this valuation lies, not necessarily a uniformizer for the valuation
EXAMPLES:
sage: ZZ.valuation(3) 3adic valuation sage: QQ.valuation(5) 5adic valuation For `p`adic rings, ``p`` has to match the `p` of the ring. sage: v = valuations.pAdicValuation(Zp(3), 2); v Traceback (most recent call last): ... ValueError: prime must be an element of positive valuation

change_domain
(ring)¶ Change the domain of this valuation to
ring
if possible.EXAMPLES:
sage: v = ZZ.valuation(2) sage: v.change_domain(QQ).domain() Rational Field

extensions
(ring)¶ Return the extensions of this valuation to
ring
.EXAMPLES:
sage: v = ZZ.valuation(2) sage: v.extensions(GaussianIntegers()) [2adic valuation]

is_totally_ramified
(G, include_steps=False, assume_squarefree=False)¶ Return whether
G
defines a single totally ramified extension of the completion of the domain of this valuation.INPUT:
G
– a monic squarefree polynomial over the domain of this valuationinclude_steps
– a boolean (default:False
); where to include the valuations produced during the process of checking whetherG
is totally ramified in the return valueassume_squarefree
– a boolean (default:False
); whether to assume thatG
is squarefree over the completion of the domain of this valuation. Setting this toTrue
can significantly improve the performance.
ALGORITHM:
This is a simplified version of
sage.rings.valuation.valuation.DiscreteValuation.mac_lane_approximants()
.EXAMPLES:
sage: k = Qp(5,4) sage: v = k.valuation() sage: R.<x> = k[] sage: G = x^2 + 1 sage: v.is_totally_ramified(G) False sage: G = x + 1 sage: v.is_totally_ramified(G) True sage: G = x^2 + 2 sage: v.is_totally_ramified(G) False sage: G = x^2 + 5 sage: v.is_totally_ramified(G) True sage: v.is_totally_ramified(G, include_steps=True) (True, [Gauss valuation induced by 5adic valuation, [ Gauss valuation induced by 5adic valuation, v((1 + O(5^4))*x) = 1/2 ]])
We consider an extension as totally ramified if its ramification index matches the degree. Hence, a trivial extension is totally ramified:
sage: R.<x> = QQ[] sage: v = QQ.valuation(2) sage: v.is_totally_ramified(x) True

is_unramified
(G, include_steps=False, assume_squarefree=False)¶ Return whether
G
defines a single unramified extension of the completion of the domain of this valuation.INPUT:
G
– a monic squarefree polynomial over the domain of this valuationinclude_steps
– a boolean (default:False
); whether to include the approximate valuations that were used to determine the result in the return value.assume_squarefree
– a boolean (default:False
); whether to assume thatG
is squarefree over the completion of the domain of this valuation. Setting this toTrue
can significantly improve the performance.
EXAMPLES:
We consider an extension as unramified if its ramification index is 1. Hence, a trivial extension is unramified:
sage: R.<x> = QQ[] sage: v = QQ.valuation(2) sage: v.is_unramified(x) True
If
G
remains irreducible in reduction, then it defines an unramified extension:sage: v.is_unramified(x^2 + x + 1) True
However, even if
G
factors, it might define an unramified extension:sage: v.is_unramified(x^2 + 2*x + 4) True

lift
(x)¶ Lift
x
from the residue field to the domain of this valuation.INPUT:
x
– an element of theresidue_field()
EXAMPLES:
sage: v = ZZ.valuation(3) sage: xbar = v.reduce(4) sage: v.lift(xbar) 1

p
()¶ Return the \(p\) of this \(p\)adic valuation.
EXAMPLES:
sage: GaussianIntegers().valuation(2).p() 2

reduce
(x)¶ Reduce
x
modulo the ideal of elements of positive valuation.INPUT:
x
– an element in the domain of this valuation
OUTPUT:
An element of the
residue_field()
.EXAMPLES:
sage: v = ZZ.valuation(3) sage: v.reduce(4) 1

restriction
(ring)¶ Return the restriction of this valuation to
ring
.EXAMPLES:
sage: v = GaussianIntegers().valuation(2) sage: v.restriction(ZZ) 2adic valuation

value_semigroup
()¶ Return the value semigroup of this valuation.
EXAMPLES:
sage: v = GaussianIntegers().valuation(2) sage: v.value_semigroup() Additive Abelian Semigroup generated by 1/2

class
sage.rings.padics.padic_valuation.
pAdicValuation_int
(parent, p)¶ Bases:
sage.rings.padics.padic_valuation.pAdicValuation_base
A \(p\)adic valuation on the integers or the rationals.
EXAMPLES:
sage: v = ZZ.valuation(3); v 3adic valuation

inverse
(x, precision)¶ Return an approximate inverse of
x
.The element returned is such that the product differs from 1 by an element of valuation at least
precision
.INPUT:
x
– an element in the domain of this valuationprecision
– a rational or infinity
EXAMPLES:
sage: v = ZZ.valuation(2) sage: x = 3 sage: y = v.inverse(3, 2); y 3 sage: x*y  1 8
This might not be possible for elements of positive valuation:
sage: v.inverse(2, 2) Traceback (most recent call last): ... ValueError: element has no approximate inverse in this ring
Unless the precision is very small:
sage: v.inverse(2, 0) 1

residue_ring
()¶ Return the residue field of this valuation.
EXAMPLES:
sage: v = ZZ.valuation(3) sage: v.residue_ring() Finite Field of size 3

simplify
(x, error=None, force=False, size_heuristic_bound=32)¶ Return a simplified version of
x
.Produce an element which differs from
x
by an element of valuation strictly greater than the valuation ofx
(or strictly greater thanerror
if set.)INPUT:
x
– an element in the domain of this valuationerror
– a rational, infinity, orNone
(default:None
), the error allowed to introduce through the simplificationforce
– ignoredsize_heuristic_bound
– whenforce
is not set, the expected factor by which thex
need to shrink to perform an actual simplification (default: 32)
EXAMPLES:
sage: v = ZZ.valuation(2) sage: v.simplify(6, force=True) 2 sage: v.simplify(6, error=0, force=True) 0
In this example, the usual rational reconstruction misses a good answer for some moduli (because the absolute value of the numerator is not bounded by the square root of the modulus):
sage: v = QQ.valuation(2) sage: v.simplify(110406, error=16, force=True) 562/19 sage: Qp(2, 16)(110406).rational_reconstruction() Traceback (most recent call last): ... ArithmeticError: rational reconstruction of 55203 (mod 65536) does not exist

uniformizer
()¶ Return a uniformizer of this \(p\)adic valuation, i.e., \(p\) as an element of the domain.
EXAMPLES:
sage: v = ZZ.valuation(3) sage: v.uniformizer() 3


class
sage.rings.padics.padic_valuation.
pAdicValuation_padic
(parent)¶ Bases:
sage.rings.padics.padic_valuation.pAdicValuation_base
The \(p\)adic valuation of a complete \(p\)adic ring.
INPUT:
R
– a \(p\)adic ring
EXAMPLES:
sage: v = Qp(2).valuation(); v #indirect doctest 2adic valuation

element_with_valuation
(v)¶ Return an element of valuation
v
.INPUT:
v
– an element of thepAdicValuation_base.value_semigroup()
of this valuation
EXAMPLES:
sage: R = Zp(3) sage: v = R.valuation() sage: v.element_with_valuation(3) 3^3 + O(3^23) sage: K = Qp(3) sage: R.<y> = K[] sage: L.<y> = K.extension(y^2 + 3*y + 3) sage: L.valuation().element_with_valuation(3/2) y^3 + O(y^43)

lift
(x)¶ Lift
x
from theresidue_field()
to the domain of this valuation.INPUT:
x
– an element of the residue field of this valuation
EXAMPLES:
sage: R = Zp(3) sage: v = R.valuation() sage: xbar = v.reduce(R(4)) sage: v.lift(xbar) 1 + O(3^20)

reduce
(x)¶ Reduce
x
modulo the ideal of elements of positive valuation.INPUT:
x
– an element of the domain of this valuation
OUTPUT:
An element of the
residue_field()
.EXAMPLES:
sage: R = Zp(3) sage: Zp(3).valuation().reduce(R(4)) 1

residue_ring
()¶ Return the residue field of this valuation.
EXAMPLES:
sage: Qq(9, names='a').valuation().residue_ring() Finite Field in a0 of size 3^2

shift
(x, s)¶ Shift
x
in its expansion with respect touniformizer()
bys
“digits”.For nonnegative
s
, this just returnsx
multiplied by a power of the uniformizer \(\pi\).For negative
s
, it does the same but when not over a field, it drops coefficients in the \(\pi\)adic expansion which have negative valuation.EXAMPLES:
sage: R = ZpCA(2) sage: v = R.valuation() sage: v.shift(R.one(), 1) 2 + O(2^20) sage: v.shift(R.one(), 1) O(2^19) sage: S.<y> = R[] sage: S.<y> = R.extension(y^3  2) sage: v = S.valuation() sage: v.shift(1, 5) y^5 + O(y^60)

simplify
(x, error=None, force=False)¶ Return a simplified version of
x
.Produce an element which differs from
x
by an element of valuation strictly greater than the valuation ofx
(or strictly greater thanerror
if set.)INPUT:
x
– an element in the domain of this valuationerror
– a rational, infinity, orNone
(default:None
), the error allowed to introduce through the simplificationforce
– ignored
EXAMPLES:
sage: R = Zp(2) sage: v = R.valuation() sage: v.simplify(6) 2 + O(2^21) sage: v.simplify(6, error=0) 0

uniformizer
()¶ Return a uniformizer of this valuation.
EXAMPLES:
sage: v = Zp(3).valuation() sage: v.uniformizer() 3 + O(3^21)