Power Series#

Sage provides an implementation of dense and sparse power series over any Sage base ring. This is the base class of the implementations of univariate and multivariate power series ring elements in Sage (see also Power Series Methods, Multivariate Power Series).

AUTHORS:

  • William Stein

  • David Harvey (2006-09-11): added solve_linear_de() method

  • Robert Bradshaw (2007-04): sqrt, rmul, lmul, shifting

  • Robert Bradshaw (2007-04): Cython version

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

EXAMPLES:

sage: R.<x> = PowerSeriesRing(ZZ)
sage: TestSuite(R).run()
sage: R([1,2,3])
1 + 2*x + 3*x^2
sage: R([1,2,3], 10)
1 + 2*x + 3*x^2 + O(x^10)
sage: f = 1 + 2*x - 3*x^3 + O(x^4); f
1 + 2*x - 3*x^3 + O(x^4)
sage: f^10
1 + 20*x + 180*x^2 + 930*x^3 + O(x^4)
sage: g = 1/f; g
1 - 2*x + 4*x^2 - 5*x^3 + O(x^4)
sage: g * f
1 + O(x^4)

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> TestSuite(R).run()
>>> R([Integer(1),Integer(2),Integer(3)])
1 + 2*x + 3*x^2
>>> R([Integer(1),Integer(2),Integer(3)], Integer(10))
1 + 2*x + 3*x^2 + O(x^10)
>>> f = Integer(1) + Integer(2)*x - Integer(3)*x**Integer(3) + O(x**Integer(4)); f
1 + 2*x - 3*x^3 + O(x^4)
>>> f**Integer(10)
1 + 20*x + 180*x^2 + 930*x^3 + O(x^4)
>>> g = Integer(1)/f; g
1 - 2*x + 4*x^2 - 5*x^3 + O(x^4)
>>> g * f
1 + O(x^4)

In Python (as opposed to Sage) create the power series ring and its generator as follows:

sage: R = PowerSeriesRing(ZZ, 'x')
sage: x = R.gen()
sage: parent(x)
Power Series Ring in x over Integer Ring

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, 'x')
>>> x = R.gen()
>>> parent(x)
Power Series Ring in x over Integer Ring

EXAMPLES:

This example illustrates that coercion for power series rings is consistent with coercion for polynomial rings.

sage: poly_ring1.<gen1> = PolynomialRing(QQ)
sage: poly_ring2.<gen2> = PolynomialRing(QQ)
sage: huge_ring.<x> = PolynomialRing(poly_ring1)

>>> from sage.all import *
>>> poly_ring1 = PolynomialRing(QQ, names=('gen1',)); (gen1,) = poly_ring1._first_ngens(1)
>>> poly_ring2 = PolynomialRing(QQ, names=('gen2',)); (gen2,) = poly_ring2._first_ngens(1)
>>> huge_ring = PolynomialRing(poly_ring1, names=('x',)); (x,) = huge_ring._first_ngens(1)

The generator of the first ring gets coerced in as itself, since it is the base ring.

sage: huge_ring(gen1)
gen1

>>> from sage.all import *
>>> huge_ring(gen1)
gen1

The generator of the second ring gets mapped via the natural map sending one generator to the other.

sage: huge_ring(gen2)
x

>>> from sage.all import *
>>> huge_ring(gen2)
x

With power series the behavior is the same.

sage: power_ring1.<gen1> = PowerSeriesRing(QQ)
sage: power_ring2.<gen2> = PowerSeriesRing(QQ)
sage: huge_power_ring.<x> = PowerSeriesRing(power_ring1)
sage: huge_power_ring(gen1)
gen1
sage: huge_power_ring(gen2)
x

>>> from sage.all import *
>>> power_ring1 = PowerSeriesRing(QQ, names=('gen1',)); (gen1,) = power_ring1._first_ngens(1)
>>> power_ring2 = PowerSeriesRing(QQ, names=('gen2',)); (gen2,) = power_ring2._first_ngens(1)
>>> huge_power_ring = PowerSeriesRing(power_ring1, names=('x',)); (x,) = huge_power_ring._first_ngens(1)
>>> huge_power_ring(gen1)
gen1
>>> huge_power_ring(gen2)
x
class sage.rings.power_series_ring_element.PowerSeries[source]#

Bases: AlgebraElement

A power series. Base class of univariate and multivariate power series. The following methods are available with both types of objects.

O(prec)[source]#

Return this series plus \(O(x^\text{prec})\). Does not change self.

EXAMPLES:

sage: R.<x> = PowerSeriesRing(ZZ)
sage: p = 1 + x^2 + x^10; p
1 + x^2 + x^10
sage: p.O(15)
1 + x^2 + x^10 + O(x^15)
sage: p.O(5)
1 + x^2 + O(x^5)
sage: p.O(-5)
Traceback (most recent call last):
...
ValueError: prec (= -5) must be non-negative

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> p = Integer(1) + x**Integer(2) + x**Integer(10); p
1 + x^2 + x^10
>>> p.O(Integer(15))
1 + x^2 + x^10 + O(x^15)
>>> p.O(Integer(5))
1 + x^2 + O(x^5)
>>> p.O(-Integer(5))
Traceback (most recent call last):
...
ValueError: prec (= -5) must be non-negative
V(n)[source]#

If \(f = \sum a_m x^m\), then this function returns \(\sum a_m x^{nm}\).

EXAMPLES:

sage: R.<x> = PowerSeriesRing(ZZ)
sage: p = 1 + x^2 + x^10; p
1 + x^2 + x^10
sage: p.V(3)
1 + x^6 + x^30
sage: (p + O(x^20)).V(3)
1 + x^6 + x^30 + O(x^60)

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> p = Integer(1) + x**Integer(2) + x**Integer(10); p
1 + x^2 + x^10
>>> p.V(Integer(3))
1 + x^6 + x^30
>>> (p + O(x**Integer(20))).V(Integer(3))
1 + x^6 + x^30 + O(x^60)
add_bigoh(prec)[source]#

Return the power series of precision at most prec got by adding \(O(q^\text{prec})\) to \(f\), where \(q\) is the variable.

EXAMPLES:

sage: R.<A> = RDF[[]]
sage: f = (1+A+O(A^5))^5; f
1.0 + 5.0*A + 10.0*A^2 + 10.0*A^3 + 5.0*A^4 + O(A^5)
sage: f.add_bigoh(3)
1.0 + 5.0*A + 10.0*A^2 + O(A^3)
sage: f.add_bigoh(5)
1.0 + 5.0*A + 10.0*A^2 + 10.0*A^3 + 5.0*A^4 + O(A^5)

>>> from sage.all import *
>>> R = RDF[['A']]; (A,) = R._first_ngens(1)
>>> f = (Integer(1)+A+O(A**Integer(5)))**Integer(5); f
1.0 + 5.0*A + 10.0*A^2 + 10.0*A^3 + 5.0*A^4 + O(A^5)
>>> f.add_bigoh(Integer(3))
1.0 + 5.0*A + 10.0*A^2 + O(A^3)
>>> f.add_bigoh(Integer(5))
1.0 + 5.0*A + 10.0*A^2 + 10.0*A^3 + 5.0*A^4 + O(A^5)
base_extend(R)[source]#

Return a copy of this power series but with coefficients in R.

The following coercion uses base_extend implicitly:

sage: R.<t> = ZZ[['t']]
sage: (t - t^2) * Mod(1, 3)
t + 2*t^2

>>> from sage.all import *
>>> R = ZZ[['t']]; (t,) = R._first_ngens(1)
>>> (t - t**Integer(2)) * Mod(Integer(1), Integer(3))
t + 2*t^2
base_ring()[source]#

Return the base ring that this power series is defined over.

EXAMPLES:

sage: R.<t> = GF(49,'alpha')[[]]                                            # needs sage.rings.finite_rings
sage: (t^2 + O(t^3)).base_ring()                                            # needs sage.rings.finite_rings
Finite Field in alpha of size 7^2

>>> from sage.all import *
>>> R = GF(Integer(49),'alpha')[['t']]; (t,) = R._first_ngens(1)# needs sage.rings.finite_rings
>>> (t**Integer(2) + O(t**Integer(3))).base_ring()                                            # needs sage.rings.finite_rings
Finite Field in alpha of size 7^2
change_ring(R)[source]#

Change if possible the coefficients of self to lie in R.

EXAMPLES:

sage: R.<T> = QQ[[]]; R
Power Series Ring in T over Rational Field
sage: f = 1 - 1/2*T + 1/3*T^2 + O(T^3)
sage: f.base_extend(GF(5))
Traceback (most recent call last):
...
TypeError: no base extension defined
sage: f.change_ring(GF(5))
1 + 2*T + 2*T^2 + O(T^3)
sage: f.change_ring(GF(3))
Traceback (most recent call last):
...
ZeroDivisionError: inverse of Mod(0, 3) does not exist

>>> from sage.all import *
>>> R = QQ[['T']]; (T,) = R._first_ngens(1); R
Power Series Ring in T over Rational Field
>>> f = Integer(1) - Integer(1)/Integer(2)*T + Integer(1)/Integer(3)*T**Integer(2) + O(T**Integer(3))
>>> f.base_extend(GF(Integer(5)))
Traceback (most recent call last):
...
TypeError: no base extension defined
>>> f.change_ring(GF(Integer(5)))
1 + 2*T + 2*T^2 + O(T^3)
>>> f.change_ring(GF(Integer(3)))
Traceback (most recent call last):
...
ZeroDivisionError: inverse of Mod(0, 3) does not exist

We can only change the ring if there is a __call__ coercion defined. The following succeeds because ZZ(K(4)) is defined.

sage: K.<a> = NumberField(cyclotomic_polynomial(3), 'a')                    # needs sage.rings.number_field
sage: R.<t> = K[['t']]                                                      # needs sage.rings.number_field
sage: (4*t).change_ring(ZZ)                                                 # needs sage.rings.number_field
4*t

>>> from sage.all import *
>>> K = NumberField(cyclotomic_polynomial(Integer(3)), 'a', names=('a',)); (a,) = K._first_ngens(1)# needs sage.rings.number_field
>>> R = K[['t']]; (t,) = R._first_ngens(1)# needs sage.rings.number_field
>>> (Integer(4)*t).change_ring(ZZ)                                                 # needs sage.rings.number_field
4*t

This does not succeed because ZZ(K(a+1)) is not defined.

sage: K.<a> = NumberField(cyclotomic_polynomial(3), 'a')                    # needs sage.rings.number_field
sage: R.<t> = K[['t']]                                                      # needs sage.rings.number_field
sage: ((a+1)*t).change_ring(ZZ)                                             # needs sage.rings.number_field
Traceback (most recent call last):
...
TypeError: Unable to coerce a + 1 to an integer

>>> from sage.all import *
>>> K = NumberField(cyclotomic_polynomial(Integer(3)), 'a', names=('a',)); (a,) = K._first_ngens(1)# needs sage.rings.number_field
>>> R = K[['t']]; (t,) = R._first_ngens(1)# needs sage.rings.number_field
>>> ((a+Integer(1))*t).change_ring(ZZ)                                             # needs sage.rings.number_field
Traceback (most recent call last):
...
TypeError: Unable to coerce a + 1 to an integer
coefficients()[source]#

Return the nonzero coefficients of self.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ)
sage: f = t + t^2 - 10/3*t^3
sage: f.coefficients()
[1, 1, -10/3]

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t + t**Integer(2) - Integer(10)/Integer(3)*t**Integer(3)
>>> f.coefficients()
[1, 1, -10/3]
common_prec(f)[source]#

Return minimum precision of \(f\) and self.

EXAMPLES:

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

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

sage: f = t + t^2 + O(t^3)
sage: g = t + t^3 + t^4 + O(t^4)
sage: f.common_prec(g)
3
sage: g.common_prec(f)
3

>>> from sage.all import *
>>> f = t + t**Integer(2) + O(t**Integer(3))
>>> g = t + t**Integer(3) + t**Integer(4) + O(t**Integer(4))
>>> f.common_prec(g)
3
>>> g.common_prec(f)
3

sage: f = t + t^2 + O(t^3)
sage: g = t^2
sage: f.common_prec(g)
3
sage: g.common_prec(f)
3

>>> from sage.all import *
>>> f = t + t**Integer(2) + O(t**Integer(3))
>>> g = t**Integer(2)
>>> f.common_prec(g)
3
>>> g.common_prec(f)
3

sage: f = t + t^2
sage: f = t^2
sage: f.common_prec(g)
+Infinity

>>> from sage.all import *
>>> f = t + t**Integer(2)
>>> f = t**Integer(2)
>>> f.common_prec(g)
+Infinity
cos(prec='infinity')[source]#

Apply cos to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: cos(f)
1 - 1/2*t^2 - t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> cos(f)
1 - 1/2*t^2 - t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: cos(f)
1 - 1/2*a^2 - a*b - 1/2*b^2 + O(a, b)^3
sage: f.cos()
1 - 1/2*a^2 - a*b - 1/2*b^2 + O(a, b)^3
sage: f.cos(prec=2)
1 + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> cos(f)
1 - 1/2*a^2 - a*b - 1/2*b^2 + O(a, b)^3
>>> f.cos()
1 - 1/2*a^2 - a*b - 1/2*b^2 + O(a, b)^3
>>> f.cos(prec=Integer(2))
1 + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2+f
sage: cos(g)
Traceback (most recent call last):
...
ValueError: can only apply cos to formal power series with zero constant term

>>> from sage.all import *
>>> g = Integer(2)+f
>>> cos(g)
Traceback (most recent call last):
...
ValueError: can only apply cos to formal power series with zero constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: cos(a)
1 - 1/2*a^2 + 1/24*a^4 - 1/720*a^6 + 1/40320*a^8 - 1/3628800*a^10 + O(a, b)^12
sage: a.cos(prec=5)
1 - 1/2*a^2 + 1/24*a^4 + O(a, b)^5
sage: cos(a + T.O(5))
1 - 1/2*a^2 + 1/24*a^4 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> cos(a)
1 - 1/2*a^2 + 1/24*a^4 - 1/720*a^6 + 1/40320*a^8 - 1/3628800*a^10 + O(a, b)^12
>>> a.cos(prec=Integer(5))
1 - 1/2*a^2 + 1/24*a^4 + O(a, b)^5
>>> cos(a + T.O(Integer(5)))
1 - 1/2*a^2 + 1/24*a^4 + O(a, b)^5
cosh(prec='infinity')[source]#

Apply cosh to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: cosh(f)
1 + 1/2*t^2 + t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> cosh(f)
1 + 1/2*t^2 + t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: cosh(f)
1 + 1/2*a^2 + a*b + 1/2*b^2 + O(a, b)^3
sage: f.cosh()
1 + 1/2*a^2 + a*b + 1/2*b^2 + O(a, b)^3
sage: f.cosh(prec=2)
1 + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> cosh(f)
1 + 1/2*a^2 + a*b + 1/2*b^2 + O(a, b)^3
>>> f.cosh()
1 + 1/2*a^2 + a*b + 1/2*b^2 + O(a, b)^3
>>> f.cosh(prec=Integer(2))
1 + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2 + f
sage: cosh(g)
Traceback (most recent call last):
...
ValueError: can only apply cosh to formal power series with zero
constant term

>>> from sage.all import *
>>> g = Integer(2) + f
>>> cosh(g)
Traceback (most recent call last):
...
ValueError: can only apply cosh to formal power series with zero
constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: cosh(a)
1 + 1/2*a^2 + 1/24*a^4 + 1/720*a^6 + 1/40320*a^8 + 1/3628800*a^10 +
 O(a, b)^12
sage: a.cosh(prec=5)
1 + 1/2*a^2 + 1/24*a^4 + O(a, b)^5
sage: cosh(a + T.O(5))
1 + 1/2*a^2 + 1/24*a^4 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> cosh(a)
1 + 1/2*a^2 + 1/24*a^4 + 1/720*a^6 + 1/40320*a^8 + 1/3628800*a^10 +
 O(a, b)^12
>>> a.cosh(prec=Integer(5))
1 + 1/2*a^2 + 1/24*a^4 + O(a, b)^5
>>> cosh(a + T.O(Integer(5)))
1 + 1/2*a^2 + 1/24*a^4 + O(a, b)^5
degree()[source]#

Return the degree of this power series, which is by definition the degree of the underlying polynomial.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ, sparse=True)
sage: f = t^100000 + O(t^10000000)
sage: f.degree()
100000

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t**Integer(100000) + O(t**Integer(10000000))
>>> f.degree()
100000
derivative(*args)[source]#

The formal derivative of this power series, with respect to variables supplied in args.

Multiple variables and iteration counts may be supplied; see documentation for the global derivative() function for more details.

See also

_derivative()

EXAMPLES:

sage: R.<x> = PowerSeriesRing(QQ)
sage: g = -x + x^2/2 - x^4 + O(x^6)
sage: g.derivative()
-1 + x - 4*x^3 + O(x^5)
sage: g.derivative(x)
-1 + x - 4*x^3 + O(x^5)
sage: g.derivative(x, x)
1 - 12*x^2 + O(x^4)
sage: g.derivative(x, 2)
1 - 12*x^2 + O(x^4)

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('x',)); (x,) = R._first_ngens(1)
>>> g = -x + x**Integer(2)/Integer(2) - x**Integer(4) + O(x**Integer(6))
>>> g.derivative()
-1 + x - 4*x^3 + O(x^5)
>>> g.derivative(x)
-1 + x - 4*x^3 + O(x^5)
>>> g.derivative(x, x)
1 - 12*x^2 + O(x^4)
>>> g.derivative(x, Integer(2))
1 - 12*x^2 + O(x^4)
egf_to_ogf()[source]#

Return the ordinary generating function power series, assuming self is an exponential generating function power series.

This is a formal Laplace transform.

This function is known as pari:serlaplace in PARI/GP.

See also

ogf_to_egf() for the inverse method.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ)
sage: f = t + t^2/factorial(2) + 2*t^3/factorial(3)
sage: f.egf_to_ogf()
t + t^2 + 2*t^3

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t + t**Integer(2)/factorial(Integer(2)) + Integer(2)*t**Integer(3)/factorial(Integer(3))
>>> f.egf_to_ogf()
t + t^2 + 2*t^3
exp(prec=None)[source]#

Return exp of this power series to the indicated precision.

INPUT:

  • prec – integer; default is self.parent().default_prec

ALGORITHM: See solve_linear_de().

Note

  • Screwy things can happen if the coefficient ring is not a field of characteristic zero. See solve_linear_de().

AUTHORS:

  • David Harvey (2006-09-08): rewrote to use simplest possible “lazy” algorithm.

  • David Harvey (2006-09-10): rewrote to use divide-and-conquer strategy.

  • David Harvey (2006-09-11): factored functionality out to solve_linear_de().

  • Sourav Sen Gupta, David Harvey (2008-11): handle constant term

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ, default_prec=10)

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(10), names=('t',)); (t,) = R._first_ngens(1)

Check that \(\exp(t)\) is, well, \(\exp(t)\):

sage: (t + O(t^10)).exp()
1 + t + 1/2*t^2 + 1/6*t^3 + 1/24*t^4 + 1/120*t^5 + 1/720*t^6
  + 1/5040*t^7 + 1/40320*t^8 + 1/362880*t^9 + O(t^10)

>>> from sage.all import *
>>> (t + O(t**Integer(10))).exp()
1 + t + 1/2*t^2 + 1/6*t^3 + 1/24*t^4 + 1/120*t^5 + 1/720*t^6
  + 1/5040*t^7 + 1/40320*t^8 + 1/362880*t^9 + O(t^10)

Check that \(\exp(\log(1+t))\) is \(1+t\):

sage: (sum([-(-t)^n/n for n in range(1, 10)]) + O(t^10)).exp()
1 + t + O(t^10)

>>> from sage.all import *
>>> (sum([-(-t)**n/n for n in range(Integer(1), Integer(10))]) + O(t**Integer(10))).exp()
1 + t + O(t^10)

Check that \(\exp(2t + t^2 - t^5)\) is whatever it is:

sage: (2*t + t^2 - t^5 + O(t^10)).exp()
1 + 2*t + 3*t^2 + 10/3*t^3 + 19/6*t^4 + 8/5*t^5 - 7/90*t^6
  - 538/315*t^7 - 425/168*t^8 - 30629/11340*t^9 + O(t^10)

>>> from sage.all import *
>>> (Integer(2)*t + t**Integer(2) - t**Integer(5) + O(t**Integer(10))).exp()
1 + 2*t + 3*t^2 + 10/3*t^3 + 19/6*t^4 + 8/5*t^5 - 7/90*t^6
  - 538/315*t^7 - 425/168*t^8 - 30629/11340*t^9 + O(t^10)

Check requesting lower precision:

sage: (t + t^2 - t^5 + O(t^10)).exp(5)
1 + t + 3/2*t^2 + 7/6*t^3 + 25/24*t^4 + O(t^5)

>>> from sage.all import *
>>> (t + t**Integer(2) - t**Integer(5) + O(t**Integer(10))).exp(Integer(5))
1 + t + 3/2*t^2 + 7/6*t^3 + 25/24*t^4 + O(t^5)

Can’t get more precision than the input:

sage: (t + t^2 + O(t^3)).exp(10)
1 + t + 3/2*t^2 + O(t^3)

>>> from sage.all import *
>>> (t + t**Integer(2) + O(t**Integer(3))).exp(Integer(10))
1 + t + 3/2*t^2 + O(t^3)

Check some boundary cases:

sage: (t + O(t^2)).exp(1)
1 + O(t)
sage: (t + O(t^2)).exp(0)
O(t^0)

>>> from sage.all import *
>>> (t + O(t**Integer(2))).exp(Integer(1))
1 + O(t)
>>> (t + O(t**Integer(2))).exp(Integer(0))
O(t^0)

Handle nonzero constant term (fixes Issue #4477):

sage: # needs sage.rings.real_mpfr
sage: R.<x> = PowerSeriesRing(RR)
sage: (1 + x + x^2 + O(x^3)).exp()
2.71828182845905 + 2.71828182845905*x + 4.07742274268857*x^2 + O(x^3)

>>> from sage.all import *
>>> # needs sage.rings.real_mpfr
>>> R = PowerSeriesRing(RR, names=('x',)); (x,) = R._first_ngens(1)
>>> (Integer(1) + x + x**Integer(2) + O(x**Integer(3))).exp()
2.71828182845905 + 2.71828182845905*x + 4.07742274268857*x^2 + O(x^3)

sage: R.<x> = PowerSeriesRing(ZZ)
sage: (1 + x + O(x^2)).exp()                                                # needs sage.symbolic
Traceback (most recent call last):
...
ArithmeticError: exponential of constant term does not belong
to coefficient ring (consider working in a larger ring)

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> (Integer(1) + x + O(x**Integer(2))).exp()                                                # needs sage.symbolic
Traceback (most recent call last):
...
ArithmeticError: exponential of constant term does not belong
to coefficient ring (consider working in a larger ring)

sage: R.<x> = PowerSeriesRing(GF(5))
sage: (1 + x + O(x^2)).exp()
Traceback (most recent call last):
...
ArithmeticError: constant term of power series does not support exponentiation

>>> from sage.all import *
>>> R = PowerSeriesRing(GF(Integer(5)), names=('x',)); (x,) = R._first_ngens(1)
>>> (Integer(1) + x + O(x**Integer(2))).exp()
Traceback (most recent call last):
...
ArithmeticError: constant term of power series does not support exponentiation
exponents()[source]#

Return the exponents appearing in self with nonzero coefficients.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ)
sage: f = t + t^2 - 10/3*t^3
sage: f.exponents()
[1, 2, 3]

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t + t**Integer(2) - Integer(10)/Integer(3)*t**Integer(3)
>>> f.exponents()
[1, 2, 3]
inverse()[source]#

Return the inverse of self, i.e., self^(-1).

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ, sparse=True)
sage: t.inverse()
t^-1
sage: type(_)
<class 'sage.rings.laurent_series_ring_element.LaurentSeries'>
sage: (1-t).inverse()
1 + t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + ...

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> t.inverse()
t^-1
>>> type(_)
<class 'sage.rings.laurent_series_ring_element.LaurentSeries'>
>>> (Integer(1)-t).inverse()
1 + t + t^2 + t^3 + t^4 + t^5 + t^6 + t^7 + t^8 + ...
is_dense()[source]#

EXAMPLES:

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

>>> 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_gen()[source]#

Return True if this is the generator (the variable) of the power series ring.

EXAMPLES:

sage: R.<t> = QQ[[]]
sage: t.is_gen()
True
sage: (1 + 2*t).is_gen()
False

>>> from sage.all import *
>>> R = QQ[['t']]; (t,) = R._first_ngens(1)
>>> t.is_gen()
True
>>> (Integer(1) + Integer(2)*t).is_gen()
False

Note that this only returns True on the actual generator, not on something that happens to be equal to it.

sage: (1*t).is_gen()
False
sage: 1*t == t
True

>>> from sage.all import *
>>> (Integer(1)*t).is_gen()
False
>>> Integer(1)*t == t
True
is_monomial()[source]#

Return True if this element is a monomial. That is, if self is \(x^n\) for some non-negative integer \(n\).

EXAMPLES:

sage: k.<z> = PowerSeriesRing(QQ, 'z')
sage: z.is_monomial()
True
sage: k(1).is_monomial()
True
sage: (z+1).is_monomial()
False
sage: (z^2909).is_monomial()
True
sage: (3*z^2909).is_monomial()
False

>>> from sage.all import *
>>> k = PowerSeriesRing(QQ, 'z', names=('z',)); (z,) = k._first_ngens(1)
>>> z.is_monomial()
True
>>> k(Integer(1)).is_monomial()
True
>>> (z+Integer(1)).is_monomial()
False
>>> (z**Integer(2909)).is_monomial()
True
>>> (Integer(3)*z**Integer(2909)).is_monomial()
False
is_sparse()[source]#

EXAMPLES:

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

>>> 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
is_square()[source]#

Return True if this function has a square root in this ring, e.g., there is an element \(y\) in self.parent() such that \(y^2\) equals self.

ALGORITHM: If the base ring is a field, this is true whenever the power series has even valuation and the leading coefficient is a perfect square.

For an integral domain, it attempts the square root in the fraction field and tests whether or not the result lies in the original ring.

EXAMPLES:

sage: K.<t> = PowerSeriesRing(QQ, 't', 5)
sage: (1+t).is_square()
True
sage: (2+t).is_square()
False
sage: (2+t.change_ring(RR)).is_square()
True
sage: t.is_square()
False
sage: K.<t> = PowerSeriesRing(ZZ, 't', 5)
sage: (1+t).is_square()
False
sage: f = (1+t)^100
sage: f.is_square()
True

>>> from sage.all import *
>>> K = PowerSeriesRing(QQ, 't', Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> (Integer(1)+t).is_square()
True
>>> (Integer(2)+t).is_square()
False
>>> (Integer(2)+t.change_ring(RR)).is_square()
True
>>> t.is_square()
False
>>> K = PowerSeriesRing(ZZ, 't', Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> (Integer(1)+t).is_square()
False
>>> f = (Integer(1)+t)**Integer(100)
>>> f.is_square()
True
is_unit()[source]#

Return True if this power series is invertible.

A power series is invertible precisely when the constant term is invertible.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(ZZ)
sage: (-1 + t - t^5).is_unit()
True
sage: (3 + t - t^5).is_unit()
False
sage: O(t^0).is_unit()
False

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> (-Integer(1) + t - t**Integer(5)).is_unit()
True
>>> (Integer(3) + t - t**Integer(5)).is_unit()
False
>>> O(t**Integer(0)).is_unit()
False

AUTHORS:

  • David Harvey (2006-09-03)

jacobi_continued_fraction()[source]#

Return the Jacobi continued fraction of self.

The J-fraction or Jacobi continued fraction of a power series is a continued fraction expansion with steps of size two. We use the following convention

\[1 / (1 + A_0 t + B_0 t^2 / (1 + A_1 t + B_1 t^2 / (1 + \cdots)))\]

OUTPUT:

tuple of pairs \((A_n, B_n)\) for \(n \geq 0\)

The expansion is done as long as possible given the precision. Whenever the expansion is not well-defined, because it would require to divide by zero, an exception is raised.

See section 2.7 of [Kra1999det] for the close relationship of this kind of expansion with Hankel determinants and orthogonal polynomials.

EXAMPLES:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: s = sum(factorial(k) * t**k for k in range(12)).O(12)
sage: s.jacobi_continued_fraction()
((-1, -1), (-3, -4), (-5, -9), (-7, -16), (-9, -25))

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> s = sum(factorial(k) * t**k for k in range(Integer(12))).O(Integer(12))
>>> s.jacobi_continued_fraction()
((-1, -1), (-3, -4), (-5, -9), (-7, -16), (-9, -25))

Another example:

sage: (log(1+t)/t).jacobi_continued_fraction()
((1/2, -1/12),
 (1/2, -1/15),
 (1/2, -9/140),
 (1/2, -4/63),
 (1/2, -25/396),
 (1/2, -9/143),
 (1/2, -49/780),
 (1/2, -16/255),
 (1/2, -81/1292))

>>> from sage.all import *
>>> (log(Integer(1)+t)/t).jacobi_continued_fraction()
((1/2, -1/12),
 (1/2, -1/15),
 (1/2, -9/140),
 (1/2, -4/63),
 (1/2, -25/396),
 (1/2, -9/143),
 (1/2, -49/780),
 (1/2, -16/255),
 (1/2, -81/1292))
laurent_series()[source]#

Return the Laurent series associated to this power series, i.e., this series considered as a Laurent series.

EXAMPLES:

sage: k.<w> = QQ[[]]
sage: f = 1 + 17*w + 15*w^3 + O(w^5)
sage: parent(f)
Power Series Ring in w over Rational Field
sage: g = f.laurent_series(); g
1 + 17*w + 15*w^3 + O(w^5)

>>> from sage.all import *
>>> k = QQ[['w']]; (w,) = k._first_ngens(1)
>>> f = Integer(1) + Integer(17)*w + Integer(15)*w**Integer(3) + O(w**Integer(5))
>>> parent(f)
Power Series Ring in w over Rational Field
>>> g = f.laurent_series(); g
1 + 17*w + 15*w^3 + O(w^5)
lift_to_precision(absprec=None)[source]#

Return a congruent power series with absolute precision at least absprec.

INPUT:

  • absprec – an integer or None (default: None), the absolute precision of the result. If None, lifts to an exact element.

EXAMPLES:

sage: A.<t> = PowerSeriesRing(GF(5))
sage: x = t + t^2 + O(t^5)
sage: x.lift_to_precision(10)
t + t^2 + O(t^10)
sage: x.lift_to_precision()
t + t^2

>>> from sage.all import *
>>> A = PowerSeriesRing(GF(Integer(5)), names=('t',)); (t,) = A._first_ngens(1)
>>> x = t + t**Integer(2) + O(t**Integer(5))
>>> x.lift_to_precision(Integer(10))
t + t^2 + O(t^10)
>>> x.lift_to_precision()
t + t^2
list()[source]#

See this method in derived classes:

Implementations MUST override this in the derived class.

EXAMPLES:

sage: from sage.rings.power_series_ring_element import PowerSeries
sage: R.<x> = PowerSeriesRing(ZZ)
sage: PowerSeries.list(1 + x^2)
Traceback (most recent call last):
...
NotImplementedError

>>> from sage.all import *
>>> from sage.rings.power_series_ring_element import PowerSeries
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> PowerSeries.list(Integer(1) + x**Integer(2))
Traceback (most recent call last):
...
NotImplementedError
log(prec=None)[source]#

Return log of this power series to the indicated precision.

This works only if the constant term of the power series is 1 or the base ring can take the logarithm of the constant coefficient.

INPUT:

  • prec – integer; default is self.parent().default_prec()

ALGORITHM: See solve_linear_de().

Warning

Screwy things can happen if the coefficient ring is not a field of characteristic zero. See solve_linear_de().

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ, default_prec=10)
sage: (1 + t + O(t^10)).log()
t - 1/2*t^2 + 1/3*t^3 - 1/4*t^4 + 1/5*t^5 - 1/6*t^6 + 1/7*t^7
  - 1/8*t^8 + 1/9*t^9 + O(t^10)

sage: t.exp().log()
t + O(t^10)

sage: (1 + t).log().exp()
1 + t + O(t^10)

sage: (-1 + t + O(t^10)).log()
Traceback (most recent call last):
...
ArithmeticError: constant term of power series is not 1

sage: # needs sage.rings.real_mpfr
sage: R.<t> = PowerSeriesRing(RR)
sage: (2 + t).log().exp()
2.00000000000000 + 1.00000000000000*t + O(t^20)

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(10), names=('t',)); (t,) = R._first_ngens(1)
>>> (Integer(1) + t + O(t**Integer(10))).log()
t - 1/2*t^2 + 1/3*t^3 - 1/4*t^4 + 1/5*t^5 - 1/6*t^6 + 1/7*t^7
  - 1/8*t^8 + 1/9*t^9 + O(t^10)

>>> t.exp().log()
t + O(t^10)

>>> (Integer(1) + t).log().exp()
1 + t + O(t^10)

>>> (-Integer(1) + t + O(t**Integer(10))).log()
Traceback (most recent call last):
...
ArithmeticError: constant term of power series is not 1

>>> # needs sage.rings.real_mpfr
>>> R = PowerSeriesRing(RR, names=('t',)); (t,) = R._first_ngens(1)
>>> (Integer(2) + t).log().exp()
2.00000000000000 + 1.00000000000000*t + O(t^20)
map_coefficients(f, new_base_ring=None)[source]#

Return the series obtained by applying f to the non-zero coefficients of self.

If f is a sage.categories.map.Map, then the resulting series will be defined over the codomain of f. Otherwise, the resulting polynomial will be over the same ring as self. Set new_base_ring to override this behaviour.

INPUT:

  • f – a callable that will be applied to the coefficients of self.

  • new_base_ring (optional) – if given, the resulting polynomial will be defined over this ring.

EXAMPLES:

sage: R.<x> = SR[[]]                                                        # needs sage.symbolic
sage: f = (1+I)*x^2 + 3*x - I                                               # needs sage.symbolic
sage: f.map_coefficients(lambda z: z.conjugate())                           # needs sage.symbolic
I + 3*x + (-I + 1)*x^2
sage: R.<x> = ZZ[[]]
sage: f = x^2 + 2
sage: f.map_coefficients(lambda a: a + 42)
44 + 43*x^2

>>> from sage.all import *
>>> R = SR[['x']]; (x,) = R._first_ngens(1)# needs sage.symbolic
>>> f = (Integer(1)+I)*x**Integer(2) + Integer(3)*x - I                                               # needs sage.symbolic
>>> f.map_coefficients(lambda z: z.conjugate())                           # needs sage.symbolic
I + 3*x + (-I + 1)*x^2
>>> R = ZZ[['x']]; (x,) = R._first_ngens(1)
>>> f = x**Integer(2) + Integer(2)
>>> f.map_coefficients(lambda a: a + Integer(42))
44 + 43*x^2

Examples with different base ring:

sage: R.<x> = ZZ[[]]
sage: k = GF(2)
sage: residue = lambda x: k(x)
sage: f = 4*x^2+x+3
sage: g = f.map_coefficients(residue); g
1 + x
sage: g.parent()
Power Series Ring in x over Integer Ring
sage: g = f.map_coefficients(residue, new_base_ring=k); g
1 + x
sage: g.parent()
Power Series Ring in x over Finite Field of size 2
sage: residue = k.coerce_map_from(ZZ)
sage: g = f.map_coefficients(residue); g
1 + x
sage: g.parent()
Power Series Ring in x over Finite Field of size 2

>>> from sage.all import *
>>> R = ZZ[['x']]; (x,) = R._first_ngens(1)
>>> k = GF(Integer(2))
>>> residue = lambda x: k(x)
>>> f = Integer(4)*x**Integer(2)+x+Integer(3)
>>> g = f.map_coefficients(residue); g
1 + x
>>> g.parent()
Power Series Ring in x over Integer Ring
>>> g = f.map_coefficients(residue, new_base_ring=k); g
1 + x
>>> g.parent()
Power Series Ring in x over Finite Field of size 2
>>> residue = k.coerce_map_from(ZZ)
>>> g = f.map_coefficients(residue); g
1 + x
>>> g.parent()
Power Series Ring in x over Finite Field of size 2

Tests other implementations:

sage: # needs sage.libs.pari
sage: R.<q> = PowerSeriesRing(GF(11), implementation='pari')
sage: f = q - q^3 + O(q^10)
sage: f.map_coefficients(lambda c: c - 2)
10*q + 8*q^3 + O(q^10)

>>> from sage.all import *
>>> # needs sage.libs.pari
>>> R = PowerSeriesRing(GF(Integer(11)), implementation='pari', names=('q',)); (q,) = R._first_ngens(1)
>>> f = q - q**Integer(3) + O(q**Integer(10))
>>> f.map_coefficients(lambda c: c - Integer(2))
10*q + 8*q^3 + O(q^10)
nth_root(n, prec=None)[source]#

Return the n-th root of this power series.

INPUT:

  • n – integer

  • prec – integer (optional); precision of the result. Though, if this series has finite precision, then the result cannot have larger precision.

EXAMPLES:

sage: R.<x> = QQ[[]]
sage: (1+x).nth_root(5)
1 + 1/5*x - 2/25*x^2 + ... + 12039376311816/2384185791015625*x^19 + O(x^20)

sage: (1 + x + O(x^5)).nth_root(5)
1 + 1/5*x - 2/25*x^2 + 6/125*x^3 - 21/625*x^4 + O(x^5)

>>> from sage.all import *
>>> R = QQ[['x']]; (x,) = R._first_ngens(1)
>>> (Integer(1)+x).nth_root(Integer(5))
1 + 1/5*x - 2/25*x^2 + ... + 12039376311816/2384185791015625*x^19 + O(x^20)

>>> (Integer(1) + x + O(x**Integer(5))).nth_root(Integer(5))
1 + 1/5*x - 2/25*x^2 + 6/125*x^3 - 21/625*x^4 + O(x^5)

Check that the results are consistent with taking log and exponential:

sage: R.<x> = PowerSeriesRing(QQ, default_prec=100)
sage: p = (1 + 2*x - x^4)**200
sage: p1 = p.nth_root(1000, prec=100)
sage: p2 = (p.log()/1000).exp()
sage: p1.prec() == p2.prec() == 100
True
sage: p1.polynomial() == p2.polynomial()
True

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(100), names=('x',)); (x,) = R._first_ngens(1)
>>> p = (Integer(1) + Integer(2)*x - x**Integer(4))**Integer(200)
>>> p1 = p.nth_root(Integer(1000), prec=Integer(100))
>>> p2 = (p.log()/Integer(1000)).exp()
>>> p1.prec() == p2.prec() == Integer(100)
True
>>> p1.polynomial() == p2.polynomial()
True

Positive characteristic:

sage: R.<u> = GF(3)[[]]
sage: p = 1 + 2 * u^2
sage: p.nth_root(4)
1 + 2*u^2 + u^6 + 2*u^8 + u^12 + 2*u^14 + O(u^20)
sage: p.nth_root(4)**4
1 + 2*u^2 + O(u^20)

>>> from sage.all import *
>>> R = GF(Integer(3))[['u']]; (u,) = R._first_ngens(1)
>>> p = Integer(1) + Integer(2) * u**Integer(2)
>>> p.nth_root(Integer(4))
1 + 2*u^2 + u^6 + 2*u^8 + u^12 + 2*u^14 + O(u^20)
>>> p.nth_root(Integer(4))**Integer(4)
1 + 2*u^2 + O(u^20)
ogf_to_egf()[source]#

Return the exponential generating function power series, assuming self is an ordinary generating function power series.

This is a formal Borel transform.

This can also be computed as serconvol(f,exp(t)) in PARI/GP.

See also

egf_to_ogf() for the inverse method.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ)
sage: f = t + t^2 + 2*t^3
sage: f.ogf_to_egf()
t + 1/2*t^2 + 1/3*t^3

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t + t**Integer(2) + Integer(2)*t**Integer(3)
>>> f.ogf_to_egf()
t + 1/2*t^2 + 1/3*t^3
padded_list(n=None)[source]#

Return a list of coefficients of self up to (but not including) \(q^n\).

Includes 0’s in the list on the right so that the list has length \(n\).

INPUT:

  • n – (optional) an integer that is at least 0. If n is not given, it will be taken to be the precision of self, unless this is +Infinity, in which case we just return self.list().

EXAMPLES:

sage: R.<q> = PowerSeriesRing(QQ)
sage: f = 1 - 17*q + 13*q^2 + 10*q^4 + O(q^7)
sage: f.list()
[1, -17, 13, 0, 10]
sage: f.padded_list(7)
[1, -17, 13, 0, 10, 0, 0]
sage: f.padded_list(10)
[1, -17, 13, 0, 10, 0, 0, 0, 0, 0]
sage: f.padded_list(3)
[1, -17, 13]
sage: f.padded_list()
[1, -17, 13, 0, 10, 0, 0]
sage: g = 1 - 17*q + 13*q^2 + 10*q^4
sage: g.list()
[1, -17, 13, 0, 10]
sage: g.padded_list()
[1, -17, 13, 0, 10]
sage: g.padded_list(10)
[1, -17, 13, 0, 10, 0, 0, 0, 0, 0]

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('q',)); (q,) = R._first_ngens(1)
>>> f = Integer(1) - Integer(17)*q + Integer(13)*q**Integer(2) + Integer(10)*q**Integer(4) + O(q**Integer(7))
>>> f.list()
[1, -17, 13, 0, 10]
>>> f.padded_list(Integer(7))
[1, -17, 13, 0, 10, 0, 0]
>>> f.padded_list(Integer(10))
[1, -17, 13, 0, 10, 0, 0, 0, 0, 0]
>>> f.padded_list(Integer(3))
[1, -17, 13]
>>> f.padded_list()
[1, -17, 13, 0, 10, 0, 0]
>>> g = Integer(1) - Integer(17)*q + Integer(13)*q**Integer(2) + Integer(10)*q**Integer(4)
>>> g.list()
[1, -17, 13, 0, 10]
>>> g.padded_list()
[1, -17, 13, 0, 10]
>>> g.padded_list(Integer(10))
[1, -17, 13, 0, 10, 0, 0, 0, 0, 0]
polynomial()[source]#

See this method in derived classes:

Implementations MUST override this in the derived class.

EXAMPLES:

sage: from sage.rings.power_series_ring_element import PowerSeries
sage: R.<x> = PowerSeriesRing(ZZ)
sage: PowerSeries.polynomial(1 + x^2)
Traceback (most recent call last):
...
NotImplementedError

>>> from sage.all import *
>>> from sage.rings.power_series_ring_element import PowerSeries
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> PowerSeries.polynomial(Integer(1) + x**Integer(2))
Traceback (most recent call last):
...
NotImplementedError
prec()[source]#

The precision of \(...+O(x^r)\) is by definition \(r\).

EXAMPLES:

sage: R.<t> = ZZ[[]]
sage: (t^2 + O(t^3)).prec()
3
sage: (1 - t^2 + O(t^100)).prec()
100

>>> from sage.all import *
>>> R = ZZ[['t']]; (t,) = R._first_ngens(1)
>>> (t**Integer(2) + O(t**Integer(3))).prec()
3
>>> (Integer(1) - t**Integer(2) + O(t**Integer(100))).prec()
100
precision_absolute()[source]#

Return the absolute precision of this series.

By definition, the absolute precision of \(...+O(x^r)\) is \(r\).

EXAMPLES:

sage: R.<t> = ZZ[[]]
sage: (t^2 + O(t^3)).precision_absolute()
3
sage: (1 - t^2 + O(t^100)).precision_absolute()
100

>>> from sage.all import *
>>> R = ZZ[['t']]; (t,) = R._first_ngens(1)
>>> (t**Integer(2) + O(t**Integer(3))).precision_absolute()
3
>>> (Integer(1) - t**Integer(2) + O(t**Integer(100))).precision_absolute()
100
precision_relative()[source]#

Return the relative precision of this series, that is the difference between its absolute precision and its valuation.

By convention, the relative precision of \(0\) (or \(O(x^r)\) for any \(r\)) is \(0\).

EXAMPLES:

sage: R.<t> = ZZ[[]]
sage: (t^2 + O(t^3)).precision_relative()
1
sage: (1 - t^2 + O(t^100)).precision_relative()
100
sage: O(t^4).precision_relative()
0

>>> from sage.all import *
>>> R = ZZ[['t']]; (t,) = R._first_ngens(1)
>>> (t**Integer(2) + O(t**Integer(3))).precision_relative()
1
>>> (Integer(1) - t**Integer(2) + O(t**Integer(100))).precision_relative()
100
>>> O(t**Integer(4)).precision_relative()
0
shift(n)[source]#

Return this power series multiplied by the power \(t^n\).

If \(n\) is negative, terms below \(t^{-n}\) are discarded.

This power series is left unchanged.

Note

Despite the fact that higher order terms are printed to the right in a power series, right shifting decreases the powers of \(t\), while left shifting increases them. This is to be consistent with polynomials, integers, etc.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ['y'], 't', 5)
sage: f = ~(1+t); f
1 - t + t^2 - t^3 + t^4 + O(t^5)
sage: f.shift(3)
t^3 - t^4 + t^5 - t^6 + t^7 + O(t^8)
sage: f >> 2
1 - t + t^2 + O(t^3)
sage: f << 10
t^10 - t^11 + t^12 - t^13 + t^14 + O(t^15)
sage: t << 29
t^30

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ['y'], 't', Integer(5), names=('t',)); (t,) = R._first_ngens(1)
>>> f = ~(Integer(1)+t); f
1 - t + t^2 - t^3 + t^4 + O(t^5)
>>> f.shift(Integer(3))
t^3 - t^4 + t^5 - t^6 + t^7 + O(t^8)
>>> f >> Integer(2)
1 - t + t^2 + O(t^3)
>>> f << Integer(10)
t^10 - t^11 + t^12 - t^13 + t^14 + O(t^15)
>>> t << Integer(29)
t^30

AUTHORS:

  • Robert Bradshaw (2007-04-18)

sin(prec='infinity')[source]#

Apply sin to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: sin(f)
t + t^2 - 1/6*t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> sin(f)
t + t^2 - 1/6*t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: sin(f)
a + b + a*b + O(a, b)^3
sage: f.sin()
a + b + a*b + O(a, b)^3
sage: f.sin(prec=2)
a + b + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> sin(f)
a + b + a*b + O(a, b)^3
>>> f.sin()
a + b + a*b + O(a, b)^3
>>> f.sin(prec=Integer(2))
a + b + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2+f
sage: sin(g)
Traceback (most recent call last):
...
ValueError: can only apply sin to formal power series with zero constant term

>>> from sage.all import *
>>> g = Integer(2)+f
>>> sin(g)
Traceback (most recent call last):
...
ValueError: can only apply sin to formal power series with zero constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: sin(a)
a - 1/6*a^3 + 1/120*a^5 - 1/5040*a^7 + 1/362880*a^9 - 1/39916800*a^11 + O(a, b)^12
sage: a.sin(prec=5)
a - 1/6*a^3 + O(a, b)^5
sage: sin(a + T.O(5))
a - 1/6*a^3 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> sin(a)
a - 1/6*a^3 + 1/120*a^5 - 1/5040*a^7 + 1/362880*a^9 - 1/39916800*a^11 + O(a, b)^12
>>> a.sin(prec=Integer(5))
a - 1/6*a^3 + O(a, b)^5
>>> sin(a + T.O(Integer(5)))
a - 1/6*a^3 + O(a, b)^5
sinh(prec='infinity')[source]#

Apply sinh to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: sinh(f)
t + t^2 + 1/6*t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> sinh(f)
t + t^2 + 1/6*t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: sinh(f)
a + b + a*b + O(a, b)^3
sage: f.sinh()
a + b + a*b + O(a, b)^3
sage: f.sinh(prec=2)
a + b + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> sinh(f)
a + b + a*b + O(a, b)^3
>>> f.sinh()
a + b + a*b + O(a, b)^3
>>> f.sinh(prec=Integer(2))
a + b + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2 + f
sage: sinh(g)
Traceback (most recent call last):
...
ValueError: can only apply sinh to formal power series with zero
constant term

>>> from sage.all import *
>>> g = Integer(2) + f
>>> sinh(g)
Traceback (most recent call last):
...
ValueError: can only apply sinh to formal power series with zero
constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: sinh(a)
a + 1/6*a^3 + 1/120*a^5 + 1/5040*a^7 + 1/362880*a^9 +
 1/39916800*a^11 + O(a, b)^12
sage: a.sinh(prec=5)
a + 1/6*a^3 + O(a, b)^5
sage: sinh(a + T.O(5))
a + 1/6*a^3 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> sinh(a)
a + 1/6*a^3 + 1/120*a^5 + 1/5040*a^7 + 1/362880*a^9 +
 1/39916800*a^11 + O(a, b)^12
>>> a.sinh(prec=Integer(5))
a + 1/6*a^3 + O(a, b)^5
>>> sinh(a + T.O(Integer(5)))
a + 1/6*a^3 + O(a, b)^5
solve_linear_de(prec='infinity', b=None, f0=None)[source]#

Obtain a power series solution to an inhomogeneous linear differential equation of the form:

\[f'(t) = a(t) f(t) + b(t).\]

INPUT:

  • self – the power series \(a(t)\)

  • b – the power series \(b(t)\) (default is zero)

  • f0 – the constant term of \(f\) (“initial condition”) (default is 1)

  • prec – desired precision of result (this will be reduced if either a or b have less precision available)

OUTPUT: the power series \(f\), to indicated precision

ALGORITHM: A divide-and-conquer strategy; see the source code. Running time is approximately \(M(n) \log n\), where \(M(n)\) is the time required for a polynomial multiplication of length \(n\) over the coefficient ring. (If you’re working over something like \(\QQ\), running time analysis can be a little complicated because the coefficients tend to explode.)

Note

  • If the coefficient ring is a field of characteristic zero, then the solution will exist and is unique.

  • For other coefficient rings, things are more complicated. A solution may not exist, and if it does it may not be unique. Generally, by the time the nth term has been computed, the algorithm will have attempted divisions by \(n!\) in the coefficient ring. So if your coefficient ring has enough ‘precision’, and if your coefficient ring can perform divisions even when the answer is not unique, and if you know in advance that a solution exists, then this function will find a solution (otherwise it will probably crash).

AUTHORS:

  • David Harvey (2006-09-11): factored functionality out from exp() function, cleaned up precision tests a bit

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ, default_prec=10)

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, default_prec=Integer(10), names=('t',)); (t,) = R._first_ngens(1)

sage: a = 2 - 3*t + 4*t^2 + O(t^10)
sage: b = 3 - 4*t^2 + O(t^7)
sage: f = a.solve_linear_de(prec=5, b=b, f0=3/5)
sage: f
 3/5 + 21/5*t + 33/10*t^2 - 38/15*t^3 + 11/24*t^4 + O(t^5)
sage: f.derivative() - a*f - b
 O(t^4)

>>> from sage.all import *
>>> a = Integer(2) - Integer(3)*t + Integer(4)*t**Integer(2) + O(t**Integer(10))
>>> b = Integer(3) - Integer(4)*t**Integer(2) + O(t**Integer(7))
>>> f = a.solve_linear_de(prec=Integer(5), b=b, f0=Integer(3)/Integer(5))
>>> f
 3/5 + 21/5*t + 33/10*t^2 - 38/15*t^3 + 11/24*t^4 + O(t^5)
>>> f.derivative() - a*f - b
 O(t^4)

sage: a = 2 - 3*t + 4*t^2
sage: b = b = 3 - 4*t^2
sage: f = a.solve_linear_de(b=b, f0=3/5)
Traceback (most recent call last):
...
ValueError: cannot solve differential equation to infinite precision

>>> from sage.all import *
>>> a = Integer(2) - Integer(3)*t + Integer(4)*t**Integer(2)
>>> b = b = Integer(3) - Integer(4)*t**Integer(2)
>>> f = a.solve_linear_de(b=b, f0=Integer(3)/Integer(5))
Traceback (most recent call last):
...
ValueError: cannot solve differential equation to infinite precision

sage: a.solve_linear_de(prec=5, b=b, f0=3/5)
 3/5 + 21/5*t + 33/10*t^2 - 38/15*t^3 + 11/24*t^4 + O(t^5)

>>> from sage.all import *
>>> a.solve_linear_de(prec=Integer(5), b=b, f0=Integer(3)/Integer(5))
 3/5 + 21/5*t + 33/10*t^2 - 38/15*t^3 + 11/24*t^4 + O(t^5)
sqrt(prec=None, extend=False, all=False, name=None)[source]#

Return a square root of self.

INPUT:

  • prec – integer (default: None): if not None and the series has infinite precision, truncates series at precision prec.

  • extend – bool (default: False); if True, return a square root in an extension ring, if necessary. Otherwise, raise a ValueError if the square root is not in the base power series ring. For example, if extend is True, the square root of a power series with odd degree leading coefficient is defined as an element of a formal extension ring.

  • name – string; if extend is True, you must also specify the print name of the formal square root.

  • all – bool (default: False); if True, return all square roots of self, instead of just one.

ALGORITHM: Newton’s method

\[x_{i+1} = \frac{1}{2}( x_i + \mathrm{self}/x_i )\]

EXAMPLES:

sage: K.<t> = PowerSeriesRing(QQ, 't', 5)
sage: sqrt(t^2)
t
sage: sqrt(1 + t)
1 + 1/2*t - 1/8*t^2 + 1/16*t^3 - 5/128*t^4 + O(t^5)
sage: sqrt(4 + t)
2 + 1/4*t - 1/64*t^2 + 1/512*t^3 - 5/16384*t^4 + O(t^5)
sage: u = sqrt(2 + t, prec=2, extend=True, name = 'alpha'); u
alpha
sage: u^2
2 + t
sage: u.parent()
Univariate Quotient Polynomial Ring in alpha
 over Power Series Ring in t over Rational Field
 with modulus x^2 - 2 - t
sage: K.<t> = PowerSeriesRing(QQ, 't', 50)
sage: sqrt(1 + 2*t + t^2)
1 + t
sage: sqrt(t^2 + 2*t^4 + t^6)
t + t^3
sage: sqrt(1 + t + t^2 + 7*t^3)^2
1 + t + t^2 + 7*t^3 + O(t^50)
sage: sqrt(K(0))
0
sage: sqrt(t^2)
t

>>> from sage.all import *
>>> K = PowerSeriesRing(QQ, 't', Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> sqrt(t**Integer(2))
t
>>> sqrt(Integer(1) + t)
1 + 1/2*t - 1/8*t^2 + 1/16*t^3 - 5/128*t^4 + O(t^5)
>>> sqrt(Integer(4) + t)
2 + 1/4*t - 1/64*t^2 + 1/512*t^3 - 5/16384*t^4 + O(t^5)
>>> u = sqrt(Integer(2) + t, prec=Integer(2), extend=True, name = 'alpha'); u
alpha
>>> u**Integer(2)
2 + t
>>> u.parent()
Univariate Quotient Polynomial Ring in alpha
 over Power Series Ring in t over Rational Field
 with modulus x^2 - 2 - t
>>> K = PowerSeriesRing(QQ, 't', Integer(50), names=('t',)); (t,) = K._first_ngens(1)
>>> sqrt(Integer(1) + Integer(2)*t + t**Integer(2))
1 + t
>>> sqrt(t**Integer(2) + Integer(2)*t**Integer(4) + t**Integer(6))
t + t^3
>>> sqrt(Integer(1) + t + t**Integer(2) + Integer(7)*t**Integer(3))**Integer(2)
1 + t + t^2 + 7*t^3 + O(t^50)
>>> sqrt(K(Integer(0)))
0
>>> sqrt(t**Integer(2))
t

sage: # needs sage.rings.complex_double
sage: K.<t> = PowerSeriesRing(CDF, 5)
sage: v = sqrt(-1 + t + t^3, all=True); v
[1.0*I - 0.5*I*t - 0.125*I*t^2 - 0.5625*I*t^3 - 0.2890625*I*t^4 + O(t^5),
 -1.0*I + 0.5*I*t + 0.125*I*t^2 + 0.5625*I*t^3 + 0.2890625*I*t^4 + O(t^5)]
sage: [a^2 for a in v]
[-1.0 + 1.0*t + 0.0*t^2 + 1.0*t^3 + O(t^5), -1.0 + 1.0*t + 0.0*t^2 + 1.0*t^3 + O(t^5)]

>>> from sage.all import *
>>> # needs sage.rings.complex_double
>>> K = PowerSeriesRing(CDF, Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> v = sqrt(-Integer(1) + t + t**Integer(3), all=True); v
[1.0*I - 0.5*I*t - 0.125*I*t^2 - 0.5625*I*t^3 - 0.2890625*I*t^4 + O(t^5),
 -1.0*I + 0.5*I*t + 0.125*I*t^2 + 0.5625*I*t^3 + 0.2890625*I*t^4 + O(t^5)]
>>> [a**Integer(2) for a in v]
[-1.0 + 1.0*t + 0.0*t^2 + 1.0*t^3 + O(t^5), -1.0 + 1.0*t + 0.0*t^2 + 1.0*t^3 + O(t^5)]

A formal square root:

sage: K.<t> = PowerSeriesRing(QQ, 5)
sage: f = 2*t + t^3 + O(t^4)
sage: s = f.sqrt(extend=True, name='sqrtf'); s
sqrtf
sage: s^2
2*t + t^3 + O(t^4)
sage: parent(s)
Univariate Quotient Polynomial Ring in sqrtf
 over Power Series Ring in t over Rational Field
 with modulus x^2 - 2*t - t^3 + O(t^4)

>>> from sage.all import *
>>> K = PowerSeriesRing(QQ, Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> f = Integer(2)*t + t**Integer(3) + O(t**Integer(4))
>>> s = f.sqrt(extend=True, name='sqrtf'); s
sqrtf
>>> s**Integer(2)
2*t + t^3 + O(t^4)
>>> parent(s)
Univariate Quotient Polynomial Ring in sqrtf
 over Power Series Ring in t over Rational Field
 with modulus x^2 - 2*t - t^3 + O(t^4)

AUTHORS:

  • Robert Bradshaw

  • William Stein

square_root()[source]#

Return the square root of self in this ring. If this cannot be done, then an error will be raised.

This function succeeds if and only if self. is_square()

EXAMPLES:

sage: K.<t> = PowerSeriesRing(QQ, 't', 5)
sage: (1 + t).square_root()
1 + 1/2*t - 1/8*t^2 + 1/16*t^3 - 5/128*t^4 + O(t^5)
sage: (2 + t).square_root()
Traceback (most recent call last):
...
ValueError: Square root does not live in this ring.
sage: (2 + t.change_ring(RR)).square_root()                                 # needs sage.rings.real_mpfr
1.41421356237309 + 0.353553390593274*t - 0.0441941738241592*t^2
 + 0.0110485434560398*t^3 - 0.00345266983001244*t^4 + O(t^5)
sage: t.square_root()
Traceback (most recent call last):
...
ValueError: Square root not defined for power series of odd valuation.
sage: K.<t> = PowerSeriesRing(ZZ, 't', 5)
sage: f = (1+t)^20
sage: f.square_root()
1 + 10*t + 45*t^2 + 120*t^3 + 210*t^4 + O(t^5)
sage: f = 1 + t
sage: f.square_root()
Traceback (most recent call last):
...
ValueError: Square root does not live in this ring.

>>> from sage.all import *
>>> K = PowerSeriesRing(QQ, 't', Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> (Integer(1) + t).square_root()
1 + 1/2*t - 1/8*t^2 + 1/16*t^3 - 5/128*t^4 + O(t^5)
>>> (Integer(2) + t).square_root()
Traceback (most recent call last):
...
ValueError: Square root does not live in this ring.
>>> (Integer(2) + t.change_ring(RR)).square_root()                                 # needs sage.rings.real_mpfr
1.41421356237309 + 0.353553390593274*t - 0.0441941738241592*t^2
 + 0.0110485434560398*t^3 - 0.00345266983001244*t^4 + O(t^5)
>>> t.square_root()
Traceback (most recent call last):
...
ValueError: Square root not defined for power series of odd valuation.
>>> K = PowerSeriesRing(ZZ, 't', Integer(5), names=('t',)); (t,) = K._first_ngens(1)
>>> f = (Integer(1)+t)**Integer(20)
>>> f.square_root()
1 + 10*t + 45*t^2 + 120*t^3 + 210*t^4 + O(t^5)
>>> f = Integer(1) + t
>>> f.square_root()
Traceback (most recent call last):
...
ValueError: Square root does not live in this ring.

AUTHORS:

  • Robert Bradshaw

stieltjes_continued_fraction()[source]#

Return the Stieltjes continued fraction of self.

The S-fraction or Stieltjes continued fraction of a power series is a continued fraction expansion with steps of size one. We use the following convention

\[1 / (1 - A_1 t / (1 - A_2 t / (1 - A_3 t / (1 - \cdots))))\]

OUTPUT:

\(A_n\) for \(n \geq 1\)

The expansion is done as long as possible given the precision. Whenever the expansion is not well-defined, because it would require to divide by zero, an exception is raised.

EXAMPLES:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: s = sum(catalan_number(k) * t**k for k in range(12)).O(12)
sage: s.stieltjes_continued_fraction()
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> s = sum(catalan_number(k) * t**k for k in range(Integer(12))).O(Integer(12))
>>> s.stieltjes_continued_fraction()
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)

Another example:

sage: (exp(t)).stieltjes_continued_fraction()
(1,
 -1/2,
 1/6,
 -1/6,
 1/10,
 -1/10,
 1/14,
 -1/14,
 1/18,
 -1/18,
 1/22,
 -1/22,
 1/26,
 -1/26,
 1/30,
 -1/30,
 1/34,
 -1/34,
 1/38)

>>> from sage.all import *
>>> (exp(t)).stieltjes_continued_fraction()
(1,
 -1/2,
 1/6,
 -1/6,
 1/10,
 -1/10,
 1/14,
 -1/14,
 1/18,
 -1/18,
 1/22,
 -1/22,
 1/26,
 -1/26,
 1/30,
 -1/30,
 1/34,
 -1/34,
 1/38)
tan(prec='infinity')[source]#

Apply tan to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: tan(f)
t + t^2 + 1/3*t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> tan(f)
t + t^2 + 1/3*t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: tan(f)
a + b + a*b + O(a, b)^3
sage: f.tan()
a + b + a*b + O(a, b)^3
sage: f.tan(prec=2)
a + b + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> tan(f)
a + b + a*b + O(a, b)^3
>>> f.tan()
a + b + a*b + O(a, b)^3
>>> f.tan(prec=Integer(2))
a + b + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2 + f
sage: tan(g)
Traceback (most recent call last):
...
ValueError: can only apply tan to formal power series with zero constant term

>>> from sage.all import *
>>> g = Integer(2) + f
>>> tan(g)
Traceback (most recent call last):
...
ValueError: can only apply tan to formal power series with zero constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: tan(a)
a + 1/3*a^3 + 2/15*a^5 + 17/315*a^7 + 62/2835*a^9 + 1382/155925*a^11 + O(a, b)^12
sage: a.tan(prec=5)
a + 1/3*a^3 + O(a, b)^5
sage: tan(a + T.O(5))
a + 1/3*a^3 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> tan(a)
a + 1/3*a^3 + 2/15*a^5 + 17/315*a^7 + 62/2835*a^9 + 1382/155925*a^11 + O(a, b)^12
>>> a.tan(prec=Integer(5))
a + 1/3*a^3 + O(a, b)^5
>>> tan(a + T.O(Integer(5)))
a + 1/3*a^3 + O(a, b)^5
tanh(prec='infinity')[source]#

Apply tanh to the formal power series.

INPUT:

  • prec – Integer or infinity. The degree to truncate the result to.

OUTPUT:

A new power series.

EXAMPLES:

For one variable:

sage: t = PowerSeriesRing(QQ, 't').gen()
sage: f = (t + t**2).O(4)
sage: tanh(f)
t + t^2 - 1/3*t^3 + O(t^4)

>>> from sage.all import *
>>> t = PowerSeriesRing(QQ, 't').gen()
>>> f = (t + t**Integer(2)).O(Integer(4))
>>> tanh(f)
t + t^2 - 1/3*t^3 + O(t^4)

For several variables:

sage: T.<a,b> = PowerSeriesRing(ZZ,2)
sage: f = a + b + a*b + T.O(3)
sage: tanh(f)
a + b + a*b + O(a, b)^3
sage: f.tanh()
a + b + a*b + O(a, b)^3
sage: f.tanh(prec=2)
a + b + O(a, b)^2

>>> from sage.all import *
>>> T = PowerSeriesRing(ZZ,Integer(2), names=('a', 'b',)); (a, b,) = T._first_ngens(2)
>>> f = a + b + a*b + T.O(Integer(3))
>>> tanh(f)
a + b + a*b + O(a, b)^3
>>> f.tanh()
a + b + a*b + O(a, b)^3
>>> f.tanh(prec=Integer(2))
a + b + O(a, b)^2

If the power series has a non-zero constant coefficient \(c\), one raises an error:

sage: g = 2 + f
sage: tanh(g)
Traceback (most recent call last):
...
ValueError: can only apply tanh to formal power series with zero
 constant term

>>> from sage.all import *
>>> g = Integer(2) + f
>>> tanh(g)
Traceback (most recent call last):
...
ValueError: can only apply tanh to formal power series with zero
 constant term

If no precision is specified, the default precision is used:

sage: T.default_prec()
12
sage: tanh(a)
a - 1/3*a^3 + 2/15*a^5 - 17/315*a^7 + 62/2835*a^9 -
1382/155925*a^11 + O(a, b)^12
sage: a.tanh(prec=5)
a - 1/3*a^3 + O(a, b)^5
sage: tanh(a + T.O(5))
a - 1/3*a^3 + O(a, b)^5

>>> from sage.all import *
>>> T.default_prec()
12
>>> tanh(a)
a - 1/3*a^3 + 2/15*a^5 - 17/315*a^7 + 62/2835*a^9 -
1382/155925*a^11 + O(a, b)^12
>>> a.tanh(prec=Integer(5))
a - 1/3*a^3 + O(a, b)^5
>>> tanh(a + T.O(Integer(5)))
a - 1/3*a^3 + O(a, b)^5
truncate(prec='infinity')[source]#

The polynomial obtained from power series by truncation.

EXAMPLES:

sage: R.<I> = GF(2)[[]]
sage: f = 1/(1+I+O(I^8)); f
1 + I + I^2 + I^3 + I^4 + I^5 + I^6 + I^7 + O(I^8)
sage: f.truncate(5)
I^4 + I^3 + I^2 + I + 1

>>> from sage.all import *
>>> R = GF(Integer(2))[['I']]; (I,) = R._first_ngens(1)
>>> f = Integer(1)/(Integer(1)+I+O(I**Integer(8))); f
1 + I + I^2 + I^3 + I^4 + I^5 + I^6 + I^7 + O(I^8)
>>> f.truncate(Integer(5))
I^4 + I^3 + I^2 + I + 1
valuation()[source]#

Return the valuation of this power series.

This is equal to the valuation of the underlying polynomial.

EXAMPLES:

Sparse examples:

sage: R.<t> = PowerSeriesRing(QQ, sparse=True)
sage: f = t^100000 + O(t^10000000)
sage: f.valuation()
100000
sage: R(0).valuation()
+Infinity

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> f = t**Integer(100000) + O(t**Integer(10000000))
>>> f.valuation()
100000
>>> R(Integer(0)).valuation()
+Infinity

Dense examples:

sage: R.<t> = PowerSeriesRing(ZZ)
sage: f = 17*t^100 + O(t^110)
sage: f.valuation()
100
sage: t.valuation()
1

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('t',)); (t,) = R._first_ngens(1)
>>> f = Integer(17)*t**Integer(100) + O(t**Integer(110))
>>> f.valuation()
100
>>> t.valuation()
1
valuation_zero_part()[source]#

Factor self as \(q^n \cdot (a_0 + a_1 q + \cdots)\) with \(a_0\) nonzero. Then this function returns \(a_0 + a_1 q + \cdots\) .

Note

This valuation zero part need not be a unit if, e.g., \(a_0\) is not invertible in the base ring.

EXAMPLES:

sage: R.<t> = PowerSeriesRing(QQ)
sage: ((1/3)*t^5*(17-2/3*t^3)).valuation_zero_part()
17/3 - 2/9*t^3

>>> from sage.all import *
>>> R = PowerSeriesRing(QQ, names=('t',)); (t,) = R._first_ngens(1)
>>> ((Integer(1)/Integer(3))*t**Integer(5)*(Integer(17)-Integer(2)/Integer(3)*t**Integer(3))).valuation_zero_part()
17/3 - 2/9*t^3

In this example the valuation 0 part is not a unit:

sage: R.<t> = PowerSeriesRing(ZZ, sparse=True)
sage: u = (-2*t^5*(17-t^3)).valuation_zero_part(); u
-34 + 2*t^3
sage: u.is_unit()
False
sage: u.valuation()
0

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, sparse=True, names=('t',)); (t,) = R._first_ngens(1)
>>> u = (-Integer(2)*t**Integer(5)*(Integer(17)-t**Integer(3))).valuation_zero_part(); u
-34 + 2*t^3
>>> u.is_unit()
False
>>> u.valuation()
0
variable()[source]#

Return a string with the name of the variable of this power series.

EXAMPLES:

sage: R.<x> = PowerSeriesRing(Rationals())
sage: f = x^2 + 3*x^4 + O(x^7)
sage: f.variable()
'x'

>>> from sage.all import *
>>> R = PowerSeriesRing(Rationals(), names=('x',)); (x,) = R._first_ngens(1)
>>> f = x**Integer(2) + Integer(3)*x**Integer(4) + O(x**Integer(7))
>>> f.variable()
'x'

AUTHORS:

  • David Harvey (2006-08-08)

sage.rings.power_series_ring_element.is_PowerSeries(x)[source]#

Return True if x is an instance of a univariate or multivariate power series.

EXAMPLES:

sage: R.<x> = PowerSeriesRing(ZZ)
sage: from sage.rings.power_series_ring_element import is_PowerSeries
sage: is_PowerSeries(1 + x^2)
True
sage: is_PowerSeries(x - x)
True
sage: is_PowerSeries(0)
False
sage: var('x')                                                                  # needs sage.symbolic
x
sage: is_PowerSeries(1 + x^2)                                                   # needs sage.symbolic
False

>>> from sage.all import *
>>> R = PowerSeriesRing(ZZ, names=('x',)); (x,) = R._first_ngens(1)
>>> from sage.rings.power_series_ring_element import is_PowerSeries
>>> is_PowerSeries(Integer(1) + x**Integer(2))
True
>>> is_PowerSeries(x - x)
True
>>> is_PowerSeries(Integer(0))
False
>>> var('x')                                                                  # needs sage.symbolic
x
>>> is_PowerSeries(Integer(1) + x**Integer(2))                                                   # needs sage.symbolic
False
sage.rings.power_series_ring_element.make_element_from_parent_v0(parent, *args)[source]#
sage.rings.power_series_ring_element.make_powerseries_poly_v0(parent, f, prec, is_gen)[source]#