Power Series Rings

Power series rings are constructed in the standard Sage fashion. See also Multivariate Power Series Rings.

EXAMPLES:

Construct rings and elements:

Sage

sage: R.<t> = PowerSeriesRing(QQ)
sage: R.random_element(6)  # random
-4 - 1/2*t^2 - 1/95*t^3 + 1/2*t^4 - 12*t^5 + O(t^6)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.random_element(Integer(6))  # random
-4 - 1/2*t^2 - 1/95*t^3 + 1/2*t^4 - 12*t^5 + O(t^6)

Sage

sage: R.<t,u,v> = PowerSeriesRing(QQ); R
Multivariate Power Series Ring in t, u, v over Rational Field
sage: p = -t + 1/2*t^3*u - 1/4*t^4*u + 2/3*v^5 + R.O(6); p
-t + 1/2*t^3*u - 1/4*t^4*u + 2/3*v^5 + O(t, u, v)^6
sage: p in R
True

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t', 'u', 'v',)); (t, u, v,) = R._first_ngens(3); R
Multivariate Power Series Ring in t, u, v over Rational Field
>>> p = -t + Integer(1)/Integer(2)*t**Integer(3)*u - Integer(1)/Integer(4)*t**Integer(4)*u + Integer(2)/Integer(3)*v**Integer(5) + R.O(Integer(6)); p
-t + 1/2*t^3*u - 1/4*t^4*u + 2/3*v^5 + O(t, u, v)^6
>>> p in R
True

The default precision is specified at construction, but does not bound the precision of created elements.

Sage

sage: R.<t> = PowerSeriesRing(QQ, default_prec=5)
sage: R.random_element(6)  # random
1/2 - 1/4*t + 2/3*t^2 - 5/2*t^3 + 2/3*t^5 + O(t^6)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(5), names=('t',)); (t,) = R._first_ngens(1)
>>> R.random_element(Integer(6))  # random
1/2 - 1/4*t + 2/3*t^2 - 5/2*t^3 + 2/3*t^5 + O(t^6)

Construct univariate power series from a list of coefficients:

Sage

sage: S = R([1, 3, 5, 7]); S
1 + 3*t + 5*t^2 + 7*t^3

Python

>>> from sage.all import *
>>> S = R([Integer(1), Integer(3), Integer(5), Integer(7)]); S
1 + 3*t + 5*t^2 + 7*t^3

The default precision of a power series ring stays fixed and cannot be changed. To work with different default precision, create a new power series ring:

Sage

sage: R.<x> = PowerSeriesRing(QQ, default_prec=10)
sage: sin(x)
x - 1/6*x^3 + 1/120*x^5 - 1/5040*x^7 + 1/362880*x^9 + O(x^10)
sage: R.<x> = PowerSeriesRing(QQ, default_prec=15)
sage: sin(x)
x - 1/6*x^3 + 1/120*x^5 - 1/5040*x^7 + 1/362880*x^9 - 1/39916800*x^11
+ 1/6227020800*x^13 + O(x^15)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(10), names=('x',)); (x,) = R._first_ngens(1)
>>> sin(x)
x - 1/6*x^3 + 1/120*x^5 - 1/5040*x^7 + 1/362880*x^9 + O(x^10)
>>> R = PowerSeriesRing(QQ, default_prec=Integer(15), names=('x',)); (x,) = R._first_ngens(1)
>>> sin(x)
x - 1/6*x^3 + 1/120*x^5 - 1/5040*x^7 + 1/362880*x^9 - 1/39916800*x^11
+ 1/6227020800*x^13 + O(x^15)

An iterated example:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: S.<t2> = PowerSeriesRing(R)
sage: S
Power Series Ring in t2 over Power Series Ring in t over Integer Ring
sage: S.base_ring()
Power Series Ring in t over Integer Ring

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> S = PowerSeriesRing(R, names=('t2',)); (t2,) = S._first_ngens(1)
>>> S
Power Series Ring in t2 over Power Series Ring in t over Integer Ring
>>> S.base_ring()
Power Series Ring in t over Integer Ring

Sage can compute with power series over the symbolic ring.

Sage

sage: # needs sage.symbolic
sage: K.<t> = PowerSeriesRing(SR, default_prec=5)
sage: a, b, c = var('a,b,c')
sage: f = a + b*t + c*t^2 + O(t^3)
sage: f*f
a^2 + 2*a*b*t + (b^2 + 2*a*c)*t^2 + O(t^3)
sage: f = sqrt(2) + sqrt(3)*t + O(t^3)
sage: f^2
2 + 2*sqrt(3)*sqrt(2)*t + 3*t^2 + O(t^3)

Python

>>> from sage.all import *
>>> # needs sage.symbolic
>>> K = PowerSeriesRing(SR, default_prec=Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> a, b, c = var('a,b,c')
>>> f = a + b*t + c*t**Integer(2) + O(t**Integer(3))
>>> f*f
a^2 + 2*a*b*t + (b^2 + 2*a*c)*t^2 + O(t^3)
>>> f = sqrt(Integer(2)) + sqrt(Integer(3))*t + O(t**Integer(3))
>>> f**Integer(2)
2 + 2*sqrt(3)*sqrt(2)*t + 3*t^2 + O(t^3)

Elements are first coerced to constants in base_ring, then coerced into the PowerSeriesRing:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: f = Mod(2, 3) * t; (f, f.parent())
(2*t, Power Series Ring in t over Ring of integers modulo 3)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = Mod(Integer(2), Integer(3)) * t; (f, f.parent())
(2*t, Power Series Ring in t over Ring of integers modulo 3)

We make a sparse power series.

Sage

sage: R.<x> = PowerSeriesRing(QQ, sparse=True); R
Sparse Power Series Ring in x over Rational Field
sage: f = 1 + x^1000000
sage: g = f*f
sage: g.degree()
2000000

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, sparse=True, names=('x',)); (x,) = R._first_ngens(1); R
Sparse Power Series Ring in x over Rational Field
>>> f = Integer(1) + x**Integer(1000000)
>>> g = f*f
>>> g.degree()
2000000

We make a sparse Laurent series from a power series generator:

Sage

sage: R.<t> = PowerSeriesRing(QQ, sparse=True)
sage: latex(-2/3*(1/t^3) + 1/t + 3/5*t^2 + O(t^5))
\frac{-\frac{2}{3}}{t^{3}} + \frac{1}{t} + \frac{3}{5}t^{2} + O(t^{5})
sage: S = parent(1/t); S
Sparse Laurent Series Ring in t over Rational Field

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> latex(-Integer(2)/Integer(3)*(Integer(1)/t**Integer(3)) + Integer(1)/t + Integer(3)/Integer(5)*t**Integer(2) + O(t**Integer(5)))
\frac{-\frac{2}{3}}{t^{3}} + \frac{1}{t} + \frac{3}{5}t^{2} + O(t^{5})
>>> S = parent(Integer(1)/t); S
Sparse Laurent Series Ring in t over Rational Field

Choose another implementation of the attached polynomial ring:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: type(t.polynomial())                                                          # needs sage.libs.flint
<... 'sage.rings.polynomial.polynomial_integer_dense_flint.Polynomial_integer_dense_flint'>
sage: S.<s> = PowerSeriesRing(ZZ, implementation='NTL')                             # needs sage.libs.ntl
sage: type(s.polynomial())                                                          # needs sage.libs.ntl
<... 'sage.rings.polynomial.polynomial_integer_dense_ntl.Polynomial_integer_dense_ntl'>

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> type(t.polynomial())                                                          # needs sage.libs.flint
<... 'sage.rings.polynomial.polynomial_integer_dense_flint.Polynomial_integer_dense_flint'>
>>> S = PowerSeriesRing(ZZ, implementation='NTL', names=('s',)); (s,) = S._first_ngens(1)# needs sage.libs.ntl
>>> type(s.polynomial())                                                          # needs sage.libs.ntl
<... 'sage.rings.polynomial.polynomial_integer_dense_ntl.Polynomial_integer_dense_ntl'>

AUTHORS:

• William Stein: the code

• Jeremy Cho (2006-05-17): some examples (above)

• Niles Johnson (2010-09): implement multivariate power series

• Simon King (2012-08): use category and coercion framework, Issue #13412

sage.rings.power_series_ring.PowerSeriesRing(base_ring, name=None, arg2=None, names=None, sparse=False, default_prec=None, order='negdeglex', num_gens=None, implementation=None)

Create a univariate or multivariate power series ring over a given (commutative) base ring.

INPUT:

• base_ring – a commutative ring

• name, names – name(s) of the indeterminate

• default_prec – the default precision used if an exact object must be changed to an approximate object in order to do an arithmetic operation. If left as None, it will be set to the global default (20) in the univariate case, and 12 in the multivariate case.

• sparse – boolean (default: False); whether power series are represented as sparse objects

• order – (default: negdeglex) term ordering, for multivariate case

• num_gens – number of generators, for multivariate case

There is a unique power series ring over each base ring with given variable name. Two power series over the same base ring with different variable names are not equal or isomorphic.

EXAMPLES (Univariate):

Sage

sage: R = PowerSeriesRing(QQ, 'x'); R
Power Series Ring in x over Rational Field

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, 'x'); R
Power Series Ring in x over Rational Field

Sage

sage: S = PowerSeriesRing(QQ, 'y'); S
Power Series Ring in y over Rational Field

Python

>>> from sage.all import *
>>> S = PowerSeriesRing(QQ, 'y'); S
Power Series Ring in y over Rational Field

Sage

sage: R = PowerSeriesRing(QQ, 10)
Traceback (most recent call last):
...
ValueError: variable name '10' does not start with a letter

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, Integer(10))
Traceback (most recent call last):
...
ValueError: variable name '10' does not start with a letter

Sage

sage: S = PowerSeriesRing(QQ, 'x', default_prec=15); S
Power Series Ring in x over Rational Field
sage: S.default_prec()
15

Python

>>> from sage.all import *
>>> S = PowerSeriesRing(QQ, 'x', default_prec=Integer(15)); S
Power Series Ring in x over Rational Field
>>> S.default_prec()
15

EXAMPLES (Multivariate) See also Multivariate Power Series Rings:

Sage

sage: R = PowerSeriesRing(QQ, 't,u,v'); R
Multivariate Power Series Ring in t, u, v over Rational Field

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, 't,u,v'); R
Multivariate Power Series Ring in t, u, v over Rational Field

Sage

sage: N = PowerSeriesRing(QQ,'w',num_gens=5); N
Multivariate Power Series Ring in w0, w1, w2, w3, w4 over Rational Field

Python

>>> from sage.all import *
>>> N = PowerSeriesRing(QQ,'w',num_gens=Integer(5)); N
Multivariate Power Series Ring in w0, w1, w2, w3, w4 over Rational Field

Number of generators can be specified before variable name without using keyword:

Sage

sage: M = PowerSeriesRing(QQ,4,'k'); M
Multivariate Power Series Ring in k0, k1, k2, k3 over Rational Field

Python

>>> from sage.all import *
>>> M = PowerSeriesRing(QQ,Integer(4),'k'); M
Multivariate Power Series Ring in k0, k1, k2, k3 over Rational Field

Multivariate power series can be constructed using angle bracket or double square bracket notation:

Sage

sage: R.<t,u,v> = PowerSeriesRing(QQ, 't,u,v'); R
Multivariate Power Series Ring in t, u, v over Rational Field

sage: ZZ[['s,t,u']]
Multivariate Power Series Ring in s, t, u over Integer Ring

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, 't,u,v', names=('t', 'u', 'v',)); (t, u, v,) = R._first_ngens(3); R
Multivariate Power Series Ring in t, u, v over Rational Field

>>> ZZ[['s,t,u']]
Multivariate Power Series Ring in s, t, u over Integer Ring

Sparse multivariate power series ring:

Sage

sage: M = PowerSeriesRing(QQ,4,'k',sparse=True); M
Sparse Multivariate Power Series Ring in k0, k1, k2, k3 over
Rational Field

Python

>>> from sage.all import *
>>> M = PowerSeriesRing(QQ,Integer(4),'k',sparse=True); M
Sparse Multivariate Power Series Ring in k0, k1, k2, k3 over
Rational Field

Power series ring over polynomial ring:

Sage

sage: H = PowerSeriesRing(PolynomialRing(ZZ,3,'z'), 4, 'f'); H
Multivariate Power Series Ring in f0, f1, f2, f3 over Multivariate
Polynomial Ring in z0, z1, z2 over Integer Ring

Python

>>> from sage.all import *
>>> H = PowerSeriesRing(PolynomialRing(ZZ,Integer(3),'z'), Integer(4), 'f'); H
Multivariate Power Series Ring in f0, f1, f2, f3 over Multivariate
Polynomial Ring in z0, z1, z2 over Integer Ring

Power series ring over finite field:

Sage

sage: S = PowerSeriesRing(GF(65537),'x,y'); S                                   # needs sage.rings.finite_rings
Multivariate Power Series Ring in x, y over Finite Field of size
65537

Python

>>> from sage.all import *
>>> S = PowerSeriesRing(GF(Integer(65537)),'x,y'); S                                   # needs sage.rings.finite_rings
Multivariate Power Series Ring in x, y over Finite Field of size
65537

Power series ring with many variables:

Sage

sage: R = PowerSeriesRing(ZZ, ['x%s'%p for p in primes(100)]); R                # needs sage.libs.pari
Multivariate Power Series Ring in x2, x3, x5, x7, x11, x13, x17, x19,
x23, x29, x31, x37, x41, x43, x47, x53, x59, x61, x67, x71, x73, x79,
x83, x89, x97 over Integer Ring

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, ['x%s'%p for p in primes(Integer(100))]); R                # needs sage.libs.pari
Multivariate Power Series Ring in x2, x3, x5, x7, x11, x13, x17, x19,
x23, x29, x31, x37, x41, x43, x47, x53, x59, x61, x67, x71, x73, x79,
x83, x89, x97 over Integer Ring

• Use inject_variables() to make the variables available for interactive use.

  Sage

  sage: R.inject_variables()                                                      # needs sage.libs.pari
  Defining x2, x3, x5, x7, x11, x13, x17, x19, x23, x29, x31, x37,
  x41, x43, x47, x53, x59, x61, x67, x71, x73, x79, x83, x89, x97
  
  sage: f = x47 + 3*x11*x29 - x19 + R.O(3)                                        # needs sage.libs.pari
  sage: f in R                                                                    # needs sage.libs.pari
  True
  

  Python

  >>> from sage.all import *
  >>> R.inject_variables()                                                      # needs sage.libs.pari
  Defining x2, x3, x5, x7, x11, x13, x17, x19, x23, x29, x31, x37,
  x41, x43, x47, x53, x59, x61, x67, x71, x73, x79, x83, x89, x97
  
  >>> f = x47 + Integer(3)*x11*x29 - x19 + R.O(Integer(3))                                        # needs sage.libs.pari
  >>> f in R                                                                    # needs sage.libs.pari
  True
  

Variable ordering determines how series are displayed:

Sage

sage: T.<a,b> = PowerSeriesRing(ZZ,order='deglex'); T
Multivariate Power Series Ring in a, b over Integer Ring
sage: T.term_order()
Degree lexicographic term order
sage: p = - 2*b^6 + a^5*b^2 + a^7 - b^2 - a*b^3 + T.O(9); p
a^7 + a^5*b^2 - 2*b^6 - a*b^3 - b^2 + O(a, b)^9

sage: U = PowerSeriesRing(ZZ,'a,b',order='negdeglex'); U
Multivariate Power Series Ring in a, b over Integer Ring
sage: U.term_order()
Negative degree lexicographic term order
sage: U(p)
-b^2 - a*b^3 - 2*b^6 + a^7 + a^5*b^2 + O(a, b)^9

Python

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,order='deglex', names=('a', 'b',)); (a, b,) = T._first_ngens(2); T
Multivariate Power Series Ring in a, b over Integer Ring
>>> T.term_order()
Degree lexicographic term order
>>> p = - Integer(2)*b**Integer(6) + a**Integer(5)*b**Integer(2) + a**Integer(7) - b**Integer(2) - a*b**Integer(3) + T.O(Integer(9)); p
a^7 + a^5*b^2 - 2*b^6 - a*b^3 - b^2 + O(a, b)^9

>>> U = PowerSeriesRing(ZZ,'a,b',order='negdeglex'); U
Multivariate Power Series Ring in a, b over Integer Ring
>>> U.term_order()
Negative degree lexicographic term order
>>> U(p)
-b^2 - a*b^3 - 2*b^6 + a^7 + a^5*b^2 + O(a, b)^9

See also

• sage.misc.defaults.set_series_precision()

class sage.rings.power_series_ring.PowerSeriesRing_domain(base_ring, name=None, default_prec=None, sparse=False, implementation=None, category=None)

Bases: PowerSeriesRing_generic, IntegralDomain

fraction_field()

Return the Laurent series ring over the fraction field of the base ring.

This is actually not the fraction field of this ring, but its completion with respect to the topology defined by the valuation. When we are working at finite precision, these two fields are indistinguishable; that is the reason why we allow ourselves to make this confusion here.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.fraction_field()
Laurent Series Ring in t over Rational Field
sage: Frac(R)
Laurent Series Ring in t over Rational Field

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.fraction_field()
Laurent Series Ring in t over Rational Field
>>> Frac(R)
Laurent Series Ring in t over Rational Field

class sage.rings.power_series_ring.PowerSeriesRing_generic(base_ring, name=None, default_prec=None, sparse=False, implementation=None, category=None)

Bases: UniqueRepresentation, Parent, Nonexact

A power series ring.

base_extend(R)

Return the power series ring over \(R\) in the same variable as self, assuming there is a canonical coerce map from the base ring of self to \(R\).

EXAMPLES:

Sage

sage: R.<T> = GF(7)[[]]; R
Power Series Ring in T over Finite Field of size 7
sage: R.change_ring(ZZ)
Power Series Ring in T over Integer Ring
sage: R.base_extend(ZZ)
Traceback (most recent call last):
...
TypeError: no base extension defined

Python

>>> from sage.all import *
>>> R = GF(Integer(7))[['T']]; (T,) = R._first_ngens(1); R
Power Series Ring in T over Finite Field of size 7
>>> R.change_ring(ZZ)
Power Series Ring in T over Integer Ring
>>> R.base_extend(ZZ)
Traceback (most recent call last):
...
TypeError: no base extension defined

change_ring(R)

Return the power series ring over \(R\) in the same variable as self.

EXAMPLES:

Sage

sage: R.<T> = QQ[[]]; R
Power Series Ring in T over Rational Field
sage: R.change_ring(GF(7))
Power Series Ring in T over Finite Field of size 7
sage: R.base_extend(GF(7))
Traceback (most recent call last):
...
TypeError: no base extension defined
sage: R.base_extend(QuadraticField(3,'a'))                                  # needs sage.rings.number_field
Power Series Ring in T over Number Field in a
 with defining polynomial x^2 - 3 with a = 1.732050807568878?

Python

>>> from sage.all import *
>>> R = QQ[['T']]; (T,) = R._first_ngens(1); R
Power Series Ring in T over Rational Field
>>> R.change_ring(GF(Integer(7)))
Power Series Ring in T over Finite Field of size 7
>>> R.base_extend(GF(Integer(7)))
Traceback (most recent call last):
...
TypeError: no base extension defined
>>> R.base_extend(QuadraticField(Integer(3),'a'))                                  # needs sage.rings.number_field
Power Series Ring in T over Number Field in a
 with defining polynomial x^2 - 3 with a = 1.732050807568878?

change_var(var)

Return the power series ring in variable var over the same base ring.

EXAMPLES:

Sage

sage: R.<T> = QQ[[]]; R
Power Series Ring in T over Rational Field
sage: R.change_var('D')
Power Series Ring in D over Rational Field

Python

>>> from sage.all import *
>>> R = QQ[['T']]; (T,) = R._first_ngens(1); R
Power Series Ring in T over Rational Field
>>> R.change_var('D')
Power Series Ring in D over Rational Field

characteristic()

Return the characteristic of this power series ring, which is the same as the characteristic of the base ring of the power series ring.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.characteristic()
0
sage: R.<w> = Integers(2^50)[[]]; R
Power Series Ring in w over Ring of integers modulo 1125899906842624
sage: R.characteristic()
1125899906842624

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.characteristic()
0
>>> R = Integers(Integer(2)**Integer(50))[['w']]; (w,) = R._first_ngens(1); R
Power Series Ring in w over Ring of integers modulo 1125899906842624
>>> R.characteristic()
1125899906842624

construction()

Return the functorial construction of self, namely, completion of the univariate polynomial ring with respect to the indeterminate (to a given precision).

EXAMPLES:

Sage

sage: R = PowerSeriesRing(ZZ, 'x')
sage: c, S = R.construction(); S
Univariate Polynomial Ring in x over Integer Ring
sage: R == c(S)
True
sage: R = PowerSeriesRing(ZZ, 'x', sparse=True)
sage: c, S = R.construction()
sage: R == c(S)
True

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, 'x')
>>> c, S = R.construction(); S
Univariate Polynomial Ring in x over Integer Ring
>>> R == c(S)
True
>>> R = PowerSeriesRing(ZZ, 'x', sparse=True)
>>> c, S = R.construction()
>>> R == c(S)
True

gen(n=0)

Return the generator of this power series ring.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.gen()
t
sage: R.gen(3)
Traceback (most recent call last):
...
IndexError: generator n>0 not defined

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.gen()
t
>>> R.gen(Integer(3))
Traceback (most recent call last):
...
IndexError: generator n>0 not defined

gens()

Return the generators of this ring.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.gens()
(t,)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.gens()
(t,)

is_dense()

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: t.is_dense()
True
sage: R.<t> = PowerSeriesRing(ZZ, sparse=True)
sage: t.is_dense()
False

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> t.is_dense()
True
>>> R = PowerSeriesRing(ZZ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> t.is_dense()
False

is_exact()

Return False since the ring of power series over any ring is not exact.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.is_exact()
False

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.is_exact()
False

is_field(proof=True)

Return False since the ring of power series over any ring is never a field.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.is_field()
False

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.is_field()
False

is_finite()

Return False since the ring of power series over any ring is never finite.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.is_finite()
False

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.is_finite()
False

is_sparse()

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ)
sage: t.is_sparse()
False
sage: R.<t> = PowerSeriesRing(ZZ, sparse=True)
sage: t.is_sparse()
True

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> t.is_sparse()
False
>>> R = PowerSeriesRing(ZZ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> t.is_sparse()
True

laurent_series_ring()

If this is the power series ring \(R[[t]]\), return the Laurent series ring \(R((t))\).

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(ZZ, default_prec=5)
sage: S = R.laurent_series_ring(); S
Laurent Series Ring in t over Integer Ring
sage: S.default_prec()
5
sage: f = 1 + t; g = 1/f; g
1 - t + t^2 - t^3 + t^4 + O(t^5)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, default_prec=Integer(5), names=('t',)); (t,) = R._first_ngens(1)
>>> S = R.laurent_series_ring(); S
Laurent Series Ring in t over Integer Ring
>>> S.default_prec()
5
>>> f = Integer(1) + t; g = Integer(1)/f; g
1 - t + t^2 - t^3 + t^4 + O(t^5)

ngens()

Return the number of generators of this power series ring.

This is always 1.

EXAMPLES:

Sage

sage: R.<t> = ZZ[[]]
sage: R.ngens()
1

Python

>>> from sage.all import *
>>> R = ZZ[['t']]; (t,) = R._first_ngens(1)
>>> R.ngens()
1

random_element(prec=None, *args, **kwds)

Return a random power series.

INPUT:

• prec – integer specifying precision of output (default: default precision of self)

• *args, **kwds – passed on to the random_element method for the base ring

OUTPUT:

Power series with precision prec whose coefficients are random elements from the base ring, randomized subject to the arguments *args and **kwds.

ALGORITHM:

Call the random_element method on the underlying polynomial ring.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(QQ)
sage: R.random_element(5)  # random
-4 - 1/2*t^2 - 1/95*t^3 + 1/2*t^4 + O(t^5)
sage: R.random_element(10)  # random
-1/2 + 2*t - 2/7*t^2 - 25*t^3 - t^4 + 2*t^5 - 4*t^7 - 1/3*t^8 - t^9 + O(t^10)

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.random_element(Integer(5))  # random
-4 - 1/2*t^2 - 1/95*t^3 + 1/2*t^4 + O(t^5)
>>> R.random_element(Integer(10))  # random
-1/2 + 2*t - 2/7*t^2 - 25*t^3 - t^4 + 2*t^5 - 4*t^7 - 1/3*t^8 - t^9 + O(t^10)

If given no argument, random_element uses default precision of self:

Sage

sage: T = PowerSeriesRing(ZZ,'t')
sage: T.default_prec()
20
sage: T.random_element()  # random
4 + 2*t - t^2 - t^3 + 2*t^4 + t^5 + t^6 - 2*t^7 - t^8 - t^9 + t^11
 - 6*t^12 + 2*t^14 + 2*t^16 - t^17 - 3*t^18 + O(t^20)
sage: S = PowerSeriesRing(ZZ,'t', default_prec=4)
sage: S.random_element()  # random
2 - t - 5*t^2 + t^3 + O(t^4)

Python

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,'t')
>>> T.default_prec()
20
>>> T.random_element()  # random
4 + 2*t - t^2 - t^3 + 2*t^4 + t^5 + t^6 - 2*t^7 - t^8 - t^9 + t^11
 - 6*t^12 + 2*t^14 + 2*t^16 - t^17 - 3*t^18 + O(t^20)
>>> S = PowerSeriesRing(ZZ,'t', default_prec=Integer(4))
>>> S.random_element()  # random
2 - t - 5*t^2 + t^3 + O(t^4)

Further arguments are passed to the underlying base ring (Issue #9481):

Sage

sage: SZ = PowerSeriesRing(ZZ,'v')
sage: SQ = PowerSeriesRing(QQ,'v')
sage: SR = PowerSeriesRing(RR,'v')

sage: SZ.random_element(x=4, y=6)  # random
4 + 5*v + 5*v^2 + 5*v^3 + 4*v^4 + 5*v^5 + 5*v^6 + 5*v^7 + 4*v^8
 + 5*v^9 + 4*v^10 + 4*v^11 + 5*v^12 + 5*v^13 + 5*v^14 + 5*v^15
 + 5*v^16 + 5*v^17 + 4*v^18 + 5*v^19 + O(v^20)
sage: SZ.random_element(3, x=4, y=6)  # random
5 + 4*v + 5*v^2 + O(v^3)
sage: SQ.random_element(3, num_bound=3, den_bound=100)  # random
1/87 - 3/70*v - 3/44*v^2 + O(v^3)
sage: SR.random_element(3, max=10, min=-10)  # random
2.85948321262904 - 9.73071330911226*v - 6.60414378519265*v^2 + O(v^3)

Python

>>> from sage.all import *
>>> SZ = PowerSeriesRing(ZZ,'v')
>>> SQ = PowerSeriesRing(QQ,'v')
>>> SR = PowerSeriesRing(RR,'v')

>>> SZ.random_element(x=Integer(4), y=Integer(6))  # random
4 + 5*v + 5*v^2 + 5*v^3 + 4*v^4 + 5*v^5 + 5*v^6 + 5*v^7 + 4*v^8
 + 5*v^9 + 4*v^10 + 4*v^11 + 5*v^12 + 5*v^13 + 5*v^14 + 5*v^15
 + 5*v^16 + 5*v^17 + 4*v^18 + 5*v^19 + O(v^20)
>>> SZ.random_element(Integer(3), x=Integer(4), y=Integer(6))  # random
5 + 4*v + 5*v^2 + O(v^3)
>>> SQ.random_element(Integer(3), num_bound=Integer(3), den_bound=Integer(100))  # random
1/87 - 3/70*v - 3/44*v^2 + O(v^3)
>>> SR.random_element(Integer(3), max=Integer(10), min=-Integer(10))  # random
2.85948321262904 - 9.73071330911226*v - 6.60414378519265*v^2 + O(v^3)

residue_field()

Return the residue field of this power series ring.

EXAMPLES:

Sage

sage: R.<x> = PowerSeriesRing(GF(17))
sage: R.residue_field()
Finite Field of size 17
sage: R.<x> = PowerSeriesRing(Zp(5))                                        # needs sage.rings.padics
sage: R.residue_field()                                                     # needs sage.rings.padics
Finite Field of size 5

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(GF(Integer(17)), names=('x',)); (x,) = R._first_ngens(1)
>>> R.residue_field()
Finite Field of size 17
>>> R = PowerSeriesRing(Zp(Integer(5)), names=('x',)); (x,) = R._first_ngens(1)# needs sage.rings.padics
>>> R.residue_field()                                                     # needs sage.rings.padics
Finite Field of size 5

uniformizer()

Return a uniformizer of this power series ring if it is a discrete valuation ring (i.e., if the base ring is actually a field). Otherwise, an error is raised.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(QQ)
sage: R.uniformizer()
t

sage: R.<t> = PowerSeriesRing(ZZ)
sage: R.uniformizer()
Traceback (most recent call last):
...
TypeError: The base ring is not a field

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.uniformizer()
t

>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> R.uniformizer()
Traceback (most recent call last):
...
TypeError: The base ring is not a field

variable_names_recursive(depth=None)

Return the list of variable names of this and its base rings.

EXAMPLES:

Sage

sage: R = QQ[['x']][['y']][['z']]
sage: R.variable_names_recursive()
('x', 'y', 'z')
sage: R.variable_names_recursive(2)
('y', 'z')

Python

>>> from sage.all import *
>>> R = QQ[['x']][['y']][['z']]
>>> R.variable_names_recursive()
('x', 'y', 'z')
>>> R.variable_names_recursive(Integer(2))
('y', 'z')

class sage.rings.power_series_ring.PowerSeriesRing_over_field(base_ring, name=None, default_prec=None, sparse=False, implementation=None, category=None)

Bases: PowerSeriesRing_domain

fraction_field()

Return the fraction field of this power series ring, which is defined since this is over a field.

This fraction field is just the Laurent series ring over the base field.

EXAMPLES:

Sage

sage: R.<t> = PowerSeriesRing(GF(7))
sage: R.fraction_field()
Laurent Series Ring in t over Finite Field of size 7
sage: Frac(R)
Laurent Series Ring in t over Finite Field of size 7

Python

>>> from sage.all import *
>>> R = PowerSeriesRing(GF(Integer(7)), names=('t',)); (t,) = R._first_ngens(1)
>>> R.fraction_field()
Laurent Series Ring in t over Finite Field of size 7
>>> Frac(R)
Laurent Series Ring in t over Finite Field of size 7

sage.rings.power_series_ring.is_PowerSeriesRing(R)

Return True if this is a univariate power series ring. This is in keeping with the behavior of is_PolynomialRing versus is_MPolynomialRing.

EXAMPLES:

Sage

sage: from sage.rings.power_series_ring import is_PowerSeriesRing
sage: is_PowerSeriesRing(10)
doctest:warning...
DeprecationWarning: The function is_PowerSeriesRing is deprecated;
use 'isinstance(..., (PowerSeriesRing_generic, LazyPowerSeriesRing) and ....ngens() == 1)' instead.
See https://github.com/sagemath/sage/issues/38290 for details.
False
sage: is_PowerSeriesRing(QQ[['x']])
True
sage: is_PowerSeriesRing(LazyPowerSeriesRing(QQ, 'x'))
True
sage: is_PowerSeriesRing(LazyPowerSeriesRing(QQ, 'x, y'))
False

Python

>>> from sage.all import *
>>> from sage.rings.power_series_ring import is_PowerSeriesRing
>>> is_PowerSeriesRing(Integer(10))
doctest:warning...
DeprecationWarning: The function is_PowerSeriesRing is deprecated;
use 'isinstance(..., (PowerSeriesRing_generic, LazyPowerSeriesRing) and ....ngens() == 1)' instead.
See https://github.com/sagemath/sage/issues/38290 for details.
False
>>> is_PowerSeriesRing(QQ[['x']])
True
>>> is_PowerSeriesRing(LazyPowerSeriesRing(QQ, 'x'))
True
>>> is_PowerSeriesRing(LazyPowerSeriesRing(QQ, 'x, y'))
False

sage.rings.power_series_ring.unpickle_power_series_ring_v0(base_ring, name, default_prec, sparse)

Unpickle (deserialize) a univariate power series ring according to the given inputs.

EXAMPLES:

Sage

sage: P.<x> = PowerSeriesRing(QQ)
sage: loads(dumps(P)) == P  # indirect doctest
True

Python

>>> from sage.all import *
>>> P = PowerSeriesRing(QQ, names=('x',)); (x,) = P._first_ngens(1)
>>> loads(dumps(P)) == P  # indirect doctest
True