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local_generic_element.pyx
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local_generic_element.pyx
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"""
Local Generic Element
This file contains a common superclass for `p`-adic elements and power
series elements.
AUTHORS:
- David Roe: initial version
- Julian Rueth (2012-10-15, 2014-06-25): added inverse_of_unit(); improved
add_bigoh()
"""
#*****************************************************************************
# Copyright (C) 2007-2013 David Roe <roed@math.harvard.edu>
# 2012-2014 Julian Rueth <julian.rueth@fsfe.org>
#
# Distributed under the terms of the GNU General Public License (GPL)
# as published by the Free Software Foundation; either version 2 of
# the License, or (at your option) any later version.
# http://www.gnu.org/licenses/
#*****************************************************************************
from sage.rings.infinity import infinity
from sage.structure.element cimport ModuleElement, RingElement, CommutativeRingElement
from sage.structure.element import coerce_binop
cdef class LocalGenericElement(CommutativeRingElement):
#cpdef _add_(self, right):
# raise NotImplementedError
cpdef _div_(self, right):
r"""
Returns the quotient of ``self`` by ``right``.
INPUT:
- ``self`` -- a `p`-adic element.
- ``right`` -- a `p`-adic element distinguishable from zero.
In a fixed-modulus ring, this element must be a unit.
EXAMPLES::
sage: R = Zp(7, 4, 'capped-rel', 'series'); R(3)/R(5)
2 + 4*7 + 5*7^2 + 2*7^3 + O(7^4)
sage: R(2/3) / R(1/3) #indirect doctest
2 + O(7^4)
sage: R(49) / R(7)
7 + O(7^5)
sage: R = Zp(7, 4, 'capped-abs', 'series'); 1/R(7)
7^-1 + O(7^2)
sage: R = Zp(7, 4, 'fixed-mod'); 1/R(7)
Traceback (most recent call last):
...
ValueError: cannot invert non-unit
"""
# this doctest doesn't actually test the function, since it's overridden.
return self * ~right
def inverse_of_unit(self):
r"""
Returns the inverse of ``self`` if ``self`` is a unit.
OUTPUT:
- an element in the same ring as ``self``
EXAMPLES::
sage: R = ZpCA(3,5)
sage: a = R(2); a
2 + O(3^5)
sage: b = a.inverse_of_unit(); b
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
A ``ZeroDivisionError`` is raised if an element has no inverse in the
ring::
sage: R(3).inverse_of_unit()
Traceback (most recent call last):
...
ZeroDivisionError: Inverse does not exist.
Unlike the usual inverse of an element, the result is in the same ring
as ``self`` and not just in its fraction field::
sage: c = ~a; c
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
sage: a.parent()
3-adic Ring with capped absolute precision 5
sage: b.parent()
3-adic Ring with capped absolute precision 5
sage: c.parent()
3-adic Field with capped relative precision 5
For fields this does of course not make any difference::
sage: R = QpCR(3,5)
sage: a = R(2)
sage: b = a.inverse_of_unit()
sage: c = ~a
sage: a.parent()
3-adic Field with capped relative precision 5
sage: b.parent()
3-adic Field with capped relative precision 5
sage: c.parent()
3-adic Field with capped relative precision 5
TESTS:
Test that this works for all kinds of p-adic base elements::
sage: ZpCA(3,5)(2).inverse_of_unit()
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
sage: ZpCR(3,5)(2).inverse_of_unit()
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
sage: ZpFM(3,5)(2).inverse_of_unit()
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
sage: QpCR(3,5)(2).inverse_of_unit()
2 + 3 + 3^2 + 3^3 + 3^4 + O(3^5)
Over unramified extensions::
sage: R = ZpCA(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 + 1 )
sage: t.inverse_of_unit()
2*t + 2*t*3 + 2*t*3^2 + 2*t*3^3 + 2*t*3^4 + O(3^5)
sage: R = ZpCR(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 + 1 )
sage: t.inverse_of_unit()
2*t + 2*t*3 + 2*t*3^2 + 2*t*3^3 + 2*t*3^4 + O(3^5)
sage: R = ZpFM(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 + 1 )
sage: t.inverse_of_unit()
2*t + 2*t*3 + 2*t*3^2 + 2*t*3^3 + 2*t*3^4 + O(3^5)
sage: R = QpCR(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 + 1 )
sage: t.inverse_of_unit()
2*t + 2*t*3 + 2*t*3^2 + 2*t*3^3 + 2*t*3^4 + O(3^5)
Over Eisenstein extensions::
sage: R = ZpCA(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 - 3 )
sage: (t - 1).inverse_of_unit()
2 + 2*t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + t^9 + O(t^10)
sage: R = ZpCR(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 - 3 )
sage: (t - 1).inverse_of_unit()
2 + 2*t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + t^9 + O(t^10)
sage: R = ZpFM(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 - 3 )
sage: (t - 1).inverse_of_unit()
2 + 2*t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + t^9 + O(t^10)
sage: R = QpCR(3,5); S.<t> = R[]; W.<t> = R.extension( t^2 - 3 )
sage: (t - 1).inverse_of_unit()
2 + 2*t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + t^9 + O(t^10)
"""
if not self.is_unit():
raise ZeroDivisionError("Inverse does not exist.")
return self.parent()(~self)
#def __getitem__(self, n):
# raise NotImplementedError
def __iter__(self):
"""
Local elements should not be iterable, so this method correspondingly
raises a ``TypeError``.
.. NOTE::
Typically, local elements provide a implementation for
``__getitem__``. If they do not provide a method ``__iter__``, then
iterating over them is realized by calling ``__getitem__``,
starting from index 0. However, there are several issues with this.
For example, terms with negative valuation would be excluded from
the iteration, and an exact value of zero would lead to an infinite
iterable.
There doesn't seem to be an obvious behaviour that iteration over
such elements should produce, so it is disabled; see :trac:`13592`.
TESTS::
sage: x = Qp(3).zero()
sage: for v in x: pass
Traceback (most recent call last):
...
TypeError: this local element is not iterable
"""
raise TypeError("this local element is not iterable")
def slice(self, i, j, k = 1):
r"""
Returns the sum of the `p^{i + l \cdot k}` terms of the series
expansion of this element, for `i + l \cdot k` between ``i`` and
``j-1`` inclusive, and nonnegative integers `l`. Behaves analogously to
the slice function for lists.
INPUT:
- ``i`` -- an integer; if set to ``None``, the sum will start with the
first non-zero term of the series.
- ``j`` -- an integer; if set to ``None`` or `\infty`, this method
behaves as if it was set to the absolute precision of this element.
- ``k`` -- (default: 1) a positive integer
EXAMPLES::
sage: R = Zp(5, 6, 'capped-rel')
sage: a = R(1/2); a
3 + 2*5 + 2*5^2 + 2*5^3 + 2*5^4 + 2*5^5 + O(5^6)
sage: a.slice(2, 4)
2*5^2 + 2*5^3 + O(5^4)
sage: a.slice(1, 6, 2)
2*5 + 2*5^3 + 2*5^5 + O(5^6)
The step size ``k`` has to be positive::
sage: a.slice(0, 3, 0)
Traceback (most recent call last):
...
ValueError: slice step must be positive
sage: a.slice(0, 3, -1)
Traceback (most recent call last):
...
ValueError: slice step must be positive
If ``i`` exceeds ``j``, then the result will be zero, with the
precision given by ``j``::
sage: a.slice(5, 4)
O(5^4)
sage: a.slice(6, 5)
O(5^5)
However, the precision can not exceed the precision of the element::
sage: a.slice(101,100)
O(5^6)
sage: a.slice(0,5,2)
3 + 2*5^2 + 2*5^4 + O(5^5)
sage: a.slice(0,6,2)
3 + 2*5^2 + 2*5^4 + O(5^6)
sage: a.slice(0,7,2)
3 + 2*5^2 + 2*5^4 + O(5^6)
If start is left blank, it is set to the valuation::
sage: K = Qp(5, 6)
sage: x = K(1/25 + 5); x
5^-2 + 5 + O(5^4)
sage: x.slice(None, 3)
5^-2 + 5 + O(5^3)
sage: x[:3]
doctest:warning
...
DeprecationWarning: __getitem__ is changing to match the behavior of number fields. Please use expansion instead.
See http://trac.sagemath.org/14825 for details.
5^-2 + 5 + O(5^3)
TESTS:
Test that slices also work over fields::
sage: a = K(1/25); a
5^-2 + O(5^4)
sage: b = K(25); b
5^2 + O(5^8)
sage: a.slice(2, 4)
O(5^4)
sage: b.slice(2, 4)
5^2 + O(5^4)
sage: a.slice(-3, -1)
5^-2 + O(5^-1)
sage: b.slice(-1, 1)
O(5)
sage: b.slice(-3, -1)
O(5^-1)
sage: b.slice(101, 100)
O(5^8)
sage: b.slice(0,7,2)
5^2 + O(5^7)
sage: b.slice(0,8,2)
5^2 + O(5^8)
sage: b.slice(0,9,2)
5^2 + O(5^8)
Verify that :trac:`14106` has been fixed::
sage: R = Zp(5,7)
sage: a = R(300)
sage: a
2*5^2 + 2*5^3 + O(5^9)
sage: a[:5]
2*5^2 + 2*5^3 + O(5^5)
sage: a.slice(None, 5, None)
2*5^2 + 2*5^3 + O(5^5)
"""
if i is None:
i = self.valuation()
if j is None or j is infinity:
j = self.precision_absolute()
if k is None:
k = 1
if k<=0:
raise ValueError("slice step must be positive")
start = i
stop = j
# for fields, self.list() contains only the coefficients starting from
# self.valuation(), so we have to shift the indices around to make up
# for this
if self.parent().is_field():
start -= self.valuation()
stop -= self.valuation()
# make sure that start and stop are non-negative
if start<0:
i += -start # fix the value of ppow below
start = 0
stop = max(stop, 0)
# the increase of the p-power in every step
pk = self.parent().uniformizer_pow(k)
# the p-power of the first term
ppow = self.parent().uniformizer_pow(i)
# construct the return value
ans = self.parent().zero()
for c in self.expansion()[start:stop:k]:
ans += ppow * c
ppow *= pk
# fix the precision of the return value
if j < ans.precision_absolute() or self.precision_absolute() < ans.precision_absolute():
ans = ans.add_bigoh(min(j,self.precision_absolute()))
return ans
def _latex_(self):
"""
Returns a latex representation of self.
EXAMPLES::
sage: R = Zp(5); a = R(17)
sage: latex(a) #indirect doctest
2 + 3 \cdot 5 + O(5^{20})
"""
# TODO: add a bunch more documentation of latexing elements
return self._repr_(do_latex = True)
#def __mod__(self, right):
# raise NotImplementedError
#cpdef _mul_(self, right):
# raise NotImplementedError
#cdef _neg_(self):
# raise NotImplementedError
#def __pow__(self, right):
# raise NotImplementedError
cpdef _sub_(self, right):
r"""
Returns the difference between ``self`` and ``right``.
EXAMPLES::
sage: R = Zp(7, 4, 'capped-rel', 'series'); a = R(12); b = R(5); a - b
7 + O(7^4)
sage: R(4/3) - R(1/3) #indirect doctest
1 + O(7^4)
"""
# this doctest doesn't actually test this function, since _sub_ is overridden.
return self + (-right)
def add_bigoh(self, absprec):
"""
Return a copy of this element with ablsolute precision decreased to
``absprec``.
INPUT:
- ``absprec`` -- an integer or positive infinity
EXAMPLES::
sage: K = QpCR(3,4)
sage: o = K(1); o
1 + O(3^4)
sage: o.add_bigoh(2)
1 + O(3^2)
sage: o.add_bigoh(-5)
O(3^-5)
One cannot use ``add_bigoh`` to lift to a higher precision; this
can be accomplished with :meth:`lift_to_precision`::
sage: o.add_bigoh(5)
1 + O(3^4)
Negative values of ``absprec`` return an element in the fraction field
of the element's parent::
sage: R = ZpCA(3,4)
sage: R(3).add_bigoh(-5)
O(3^-5)
For fixed-mod elements this method truncates the element::
sage: R = ZpFM(3,4)
sage: R(3).add_bigoh(1)
O(3^4)
If ``absprec`` exceeds the precision of the element, then this method
has no effect::
sage: R(3).add_bigoh(5)
3 + O(3^4)
A negative value for ``absprec`` returns an element in the fraction field::
sage: R(3).add_bigoh(-1).parent()
3-adic Field with floating precision 4
TESTS:
Test that this also works for infinity::
sage: R = ZpCR(3,4)
sage: R(3).add_bigoh(infinity)
3 + O(3^5)
sage: R(0).add_bigoh(infinity)
0
"""
parent = self.parent()
if absprec >= self.precision_absolute():
return self
if absprec < 0:
parent = parent.fraction_field()
return parent(self, absprec=absprec)
#def copy(self):
# raise NotImplementedError
#def exp(self):
# raise NotImplementedError
def is_integral(self):
"""
Returns whether self is an integral element.
INPUT:
- ``self`` -- a local ring element
OUTPUT:
- boolean -- whether ``self`` is an integral element.
EXAMPLES::
sage: R = Qp(3,20)
sage: a = R(7/3); a.is_integral()
False
sage: b = R(7/5); b.is_integral()
True
"""
return self.valuation() >= 0
#def is_square(self):
# raise NotImplementedError
def is_padic_unit(self):
"""
Returns whether self is a `p`-adic unit. That is, whether it has zero valuation.
INPUT:
- ``self`` -- a local ring element
OUTPUT:
- boolean -- whether ``self`` is a unit
EXAMPLES::
sage: R = Zp(3,20,'capped-rel'); K = Qp(3,20,'capped-rel')
sage: R(0).is_padic_unit()
False
sage: R(1).is_padic_unit()
True
sage: R(2).is_padic_unit()
True
sage: R(3).is_padic_unit()
False
sage: Qp(5,5)(5).is_padic_unit()
False
TESTS::
sage: R(4).is_padic_unit()
True
sage: R(6).is_padic_unit()
False
sage: R(9).is_padic_unit()
False
sage: K(0).is_padic_unit()
False
sage: K(1).is_padic_unit()
True
sage: K(2).is_padic_unit()
True
sage: K(3).is_padic_unit()
False
sage: K(4).is_padic_unit()
True
sage: K(6).is_padic_unit()
False
sage: K(9).is_padic_unit()
False
sage: K(1/3).is_padic_unit()
False
sage: K(1/9).is_padic_unit()
False
sage: Qq(3^2,5,names='a')(3).is_padic_unit()
False
"""
return self.valuation() == 0
def is_unit(self):
"""
Returns whether self is a unit
INPUT:
- ``self`` -- a local ring element
OUTPUT:
- boolean -- whether ``self`` is a unit
NOTES:
For fields all nonzero elements are units. For DVR's, only those elements of valuation 0 are. An older implementation ignored the case of fields, and returned always the negation of self.valuation()==0. This behavior is now supported with self.is_padic_unit().
EXAMPLES::
sage: R = Zp(3,20,'capped-rel'); K = Qp(3,20,'capped-rel')
sage: R(0).is_unit()
False
sage: R(1).is_unit()
True
sage: R(2).is_unit()
True
sage: R(3).is_unit()
False
sage: Qp(5,5)(5).is_unit() # Note that 5 is invertible in `QQ_5`, even if it has positive valuation!
True
sage: Qp(5,5)(5).is_padic_unit()
False
TESTS::
sage: R(4).is_unit()
True
sage: R(6).is_unit()
False
sage: R(9).is_unit()
False
sage: K(0).is_unit()
False
sage: K(1).is_unit()
True
sage: K(2).is_unit()
True
sage: K(3).is_unit()
True
sage: K(4).is_unit()
True
sage: K(6).is_unit()
True
sage: K(9).is_unit()
True
sage: K(1/3).is_unit()
True
sage: K(1/9).is_unit()
True
sage: Qq(3^2,5,names='a')(3).is_unit()
True
sage: R(0,0).is_unit()
False
sage: K(0,0).is_unit()
False
"""
if self.is_zero():
return False
if self.parent().is_field():
return True
return self.valuation() == 0
#def is_zero(self, prec):
# raise NotImplementedError
#def is_equal_to(self, right, prec):
# raise NotImplementedError
#def lift(self):
# raise NotImplementedError
#def list(self):
# raise NotImplementedError
#def log(self):
# raise NotImplementedError
#def multiplicative_order(self, prec):
# raise NotImplementedError
#def padded_list(self):
# raise NotImplementedError
#def precision_absolute(self):
# raise NotImplementedError
#def precision_relative(self):
# raise NotImplementedError
#def residue(self, prec):
# raise NotImplementedError
def sqrt(self, extend = True, all = False):
r"""
TODO: document what "extend" and "all" do
INPUT:
- ``self`` -- a local ring element
OUTPUT:
- local ring element -- the square root of ``self``
EXAMPLES::
sage: R = Zp(13, 10, 'capped-rel', 'series')
sage: a = sqrt(R(-1)); a * a
12 + 12*13 + 12*13^2 + 12*13^3 + 12*13^4 + 12*13^5 + 12*13^6 + 12*13^7 + 12*13^8 + 12*13^9 + O(13^10)
sage: sqrt(R(4))
2 + O(13^10)
sage: sqrt(R(4/9)) * 3
2 + O(13^10)
"""
return self.square_root(extend, all)
#def square_root(self, extend = True, all = False):
# raise NotImplementedError
#def unit_part(self):
# raise NotImplementedError
#def valuation(self):
# raise NotImplementedError
def normalized_valuation(self):
r"""
Returns the normalized valuation of this local ring element,
i.e., the valuation divided by the absolute ramification index.
INPUT:
``self`` -- a local ring element.
OUTPUT:
rational -- the normalized valuation of ``self``.
EXAMPLES::
sage: Q7 = Qp(7)
sage: R.<x> = Q7[]
sage: F.<z> = Q7.ext(x^3+7*x+7)
sage: z.normalized_valuation()
1/3
"""
F = self.parent()
return self.valuation()/F.ramification_index()
def _min_valuation(self):
r"""
Returns the valuation of this local ring element.
This function only differs from valuation for lazy elements.
INPUT:
- ``self`` -- a local ring element.
OUTPUT:
- integer -- the valuation of ``self``.
EXAMPLES::
sage: R = Qp(7, 4, 'capped-rel', 'series')
sage: R(7)._min_valuation()
1
sage: R(1/7)._min_valuation()
-1
"""
return self.valuation()
def euclidean_degree(self):
r"""
Return the degree of this element as an element of an Euclidean domain.
EXAMPLES:
For a field, this is always zero except for the zero element::
sage: K = Qp(2)
sage: K.one().euclidean_degree()
0
sage: K.gen().euclidean_degree()
0
sage: K.zero().euclidean_degree()
Traceback (most recent call last):
...
ValueError: euclidean degree not defined for the zero element
For a ring which is not a field, this is the valuation of the element::
sage: R = Zp(2)
sage: R.one().euclidean_degree()
0
sage: R.gen().euclidean_degree()
1
sage: R.zero().euclidean_degree()
Traceback (most recent call last):
...
ValueError: euclidean degree not defined for the zero element
"""
if self.is_zero():
raise ValueError("euclidean degree not defined for the zero element")
from sage.categories.fields import Fields
if self.parent() in Fields():
from sage.rings.all import Integer
return Integer(0)
return self.valuation()
@coerce_binop
def quo_rem(self, other):
r"""
Return the quotient with remainder of the division of this element by
``other``.
INPUT:
- ``other`` -- an element in the same ring
EXAMPLES::
sage: R = Zp(3, 5)
sage: R(12).quo_rem(R(2))
(2*3 + O(3^6), 0)
sage: R(2).quo_rem(R(12))
(0, 2 + O(3^5))
sage: K = Qp(3, 5)
sage: K(12).quo_rem(K(2))
(2*3 + O(3^6), 0)
sage: K(2).quo_rem(K(12))
(2*3^-1 + 1 + 3 + 3^2 + 3^3 + O(3^4), 0)
"""
if other.is_zero():
raise ZeroDivisionError
from sage.categories.fields import Fields
if self.parent() in Fields():
return (self / other, self.parent().zero())
if self.valuation() < other.valuation():
return (self.parent().zero(), self)
return ( (self>>other.valuation())*other.unit_part().inverse_of_unit(),
self.parent().zero() )
def _test_trivial_powers(self, **options):
r"""
Check that taking trivial powers of elements works as expected.
EXAMPLES::
sage: x = Zp(3, 5).zero()
sage: x._test_trivial_powers()
"""
tester = self._tester(**options)
x = self**1
tester.assertEqual(x, self)
tester.assertEqual(x.precision_absolute(), self.precision_absolute())
z = self**0
one = self.parent().one()
tester.assertEqual(z, one)
tester.assertEqual(z.precision_absolute(), one.precision_absolute())