Elements of Laurent polynomial rings

class sage.rings.polynomial.laurent_polynomial.LaurentPolynomial

Bases: CommutativeAlgebraElement

Base class for Laurent polynomials.

change_ring(R)

Return a copy of this Laurent polynomial, with coefficients in R.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: a = x^2 + 3*x^3 + 5*x^-1
sage: a.change_ring(GF(3))
2*x^-1 + x^2

Check that github issue #22277 is fixed:

sage: R.<x, y> = LaurentPolynomialRing(QQ)                                  # needs sage.modules
sage: a = 2*x^2 + 3*x^3 + 4*x^-1                                            # needs sage.modules
sage: a.change_ring(GF(3))                                                  # needs sage.modules
-x^2 + x^-1

dict()

Abstract dict method.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: from sage.rings.polynomial.laurent_polynomial import LaurentPolynomial
sage: LaurentPolynomial.dict(x)
Traceback (most recent call last):
...
NotImplementedError

hamming_weight()

Return the hamming weight of self.

The hamming weight is number of non-zero coefficients and also known as the weight or sparsity.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: f = x^3 - 1
sage: f.hamming_weight()
2

map_coefficients(f, new_base_ring=None)

Apply f to the coefficients of self.

If f is a sage.categories.map.Map, then the resulting polynomial 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 behavior.

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: # needs sage.rings.finite_rings
sage: k.<a> = GF(9)
sage: R.<x> = LaurentPolynomialRing(k)
sage: f = x*a + a
sage: f.map_coefficients(lambda a: a + 1)
(a + 1) + (a + 1)*x
sage: R.<x,y> = LaurentPolynomialRing(k, 2)
sage: f = x*a + 2*x^3*y*a + a
sage: f.map_coefficients(lambda a: a + 1)
(2*a + 1)*x^3*y + (a + 1)*x + a + 1

Examples with different base ring:

sage: # needs sage.modules sage.rings.finite_rings
sage: R.<r> = GF(9); S.<s> = GF(81)
sage: h = Hom(R, S)[0]; h
Ring morphism:
  From: Finite Field in r of size 3^2
  To:   Finite Field in s of size 3^4
  Defn: r |--> 2*s^3 + 2*s^2 + 1
sage: T.<X,Y> = LaurentPolynomialRing(R, 2)
sage: f = r*X + Y
sage: g = f.map_coefficients(h); g
(2*s^3 + 2*s^2 + 1)*X + Y
sage: g.parent()
Multivariate Laurent Polynomial Ring in X, Y
 over Finite Field in s of size 3^4
sage: h = lambda x: x.trace()
sage: g = f.map_coefficients(h); g
X - Y
sage: g.parent()
Multivariate Laurent Polynomial Ring in X, Y
 over Finite Field in r of size 3^2
sage: g = f.map_coefficients(h, new_base_ring=GF(3)); g
X - Y
sage: g.parent()
Multivariate Laurent Polynomial Ring in X, Y over Finite Field of size 3

number_of_terms()

Abstract method for number of terms

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: from sage.rings.polynomial.laurent_polynomial import LaurentPolynomial
sage: LaurentPolynomial.number_of_terms(x)
Traceback (most recent call last):
...
NotImplementedError

class sage.rings.polynomial.laurent_polynomial.LaurentPolynomial_univariate

Bases: LaurentPolynomial

A univariate Laurent polynomial in the form of \(t^n \cdot f\) where \(f\) is a polynomial in \(t\).

INPUT:

• parent – a Laurent polynomial ring

• f – a polynomial (or something can be coerced to one)

• n – (default: 0) an integer

AUTHORS:

• Tom Boothby (2011) copied this class almost verbatim from laurent_series_ring_element.pyx, so most of the credit goes to William Stein, David Joyner, and Robert Bradshaw

• Travis Scrimshaw (09-2013): Cleaned-up and added a few extra methods

coefficients()

Return the nonzero coefficients of self.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: f = -5/t^(2) + t + t^2 - 10/3*t^3
sage: f.coefficients()
[-5, 1, 1, -10/3]

constant_coefficient()

Return the coefficient of the constant term of self.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: f = 3*t^-2 - t^-1 + 3 + t^2
sage: f.constant_coefficient()
3
sage: g = -2*t^-2 + t^-1 + 3*t
sage: g.constant_coefficient()
0

degree()

Return the degree of self.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: g = x^2 - x^4
sage: g.degree()
4
sage: g = -10/x^5 + x^2 - x^7
sage: g.degree()
7

derivative(*args)

The formal derivative of this Laurent polynomial, 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> = LaurentPolynomialRing(QQ)
sage: g = 1/x^10 - x + x^2 - x^4
sage: g.derivative()
-10*x^-11 - 1 + 2*x - 4*x^3
sage: g.derivative(x)
-10*x^-11 - 1 + 2*x - 4*x^3

sage: R.<t> = PolynomialRing(ZZ)
sage: S.<x> = LaurentPolynomialRing(R)
sage: f = 2*t/x + (3*t^2 + 6*t)*x
sage: f.derivative()
-2*t*x^-2 + (3*t^2 + 6*t)
sage: f.derivative(x)
-2*t*x^-2 + (3*t^2 + 6*t)
sage: f.derivative(t)
2*x^-1 + (6*t + 6)*x

dict()

Return a dictionary representing self.

EXAMPLES:

sage: R.<x,y> = ZZ[]
sage: Q.<t> = LaurentPolynomialRing(R)
sage: f = (x^3 + y/t^3)^3 + t^2; f
y^3*t^-9 + 3*x^3*y^2*t^-6 + 3*x^6*y*t^-3 + x^9 + t^2
sage: f.dict()
{-9: y^3, -6: 3*x^3*y^2, -3: 3*x^6*y, 0: x^9, 2: 1}

exponents()

Return the exponents appearing in self with nonzero coefficients.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: f = -5/t^(2) + t + t^2 - 10/3*t^3
sage: f.exponents()
[-2, 1, 2, 3]

factor()

Return a Laurent monomial (the unit part of the factorization) and a factored polynomial.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(ZZ)
sage: f = 4*t^-7 + 3*t^3 + 2*t^4 + t^-6
sage: f.factor()                                                            # needs sage.libs.pari
(t^-7) * (4 + t + 3*t^10 + 2*t^11)

gcd(right)

Return the gcd of self with right where the common divisor d makes both self and right into polynomials with the lowest possible degree.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: t.gcd(2)
1
sage: gcd(t^-2 + 1, t^-4 + 3*t^-1)
t^-4
sage: gcd((t^-2 + t)*(t + t^-1), (t^5 + t^8)*(1 + t^-2))
t^-3 + t^-1 + 1 + t^2

integral()

The formal integral of this Laurent series with 0 constant term.

EXAMPLES:

The integral may or may not be defined if the base ring is not a field.

sage: t = LaurentPolynomialRing(ZZ, 't').0
sage: f = 2*t^-3 + 3*t^2
sage: f.integral()
-t^-2 + t^3

sage: f = t^3
sage: f.integral()
Traceback (most recent call last):
...
ArithmeticError: coefficients of integral cannot be coerced into the base ring

The integral of \(1/t\) is \(\log(t)\), which is not given by a Laurent polynomial:

sage: t = LaurentPolynomialRing(ZZ,'t').0
sage: f = -1/t^3 - 31/t
sage: f.integral()
Traceback (most recent call last):
...
ArithmeticError: the integral of is not a Laurent polynomial, since t^-1 has nonzero coefficient

Another example with just one negative coefficient:

sage: A.<t> = LaurentPolynomialRing(QQ)
sage: f = -2*t^(-4)
sage: f.integral()
2/3*t^-3
sage: f.integral().derivative() == f
True

inverse_of_unit()

Return the inverse of self if a unit.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: (t^-2).inverse_of_unit()
t^2
sage: (t + 2).inverse_of_unit()
Traceback (most recent call last):
...
ArithmeticError: element is not a unit

is_constant()

Return whether this Laurent polynomial is constant.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: x.is_constant()
False
sage: R.one().is_constant()
True
sage: (x^-2).is_constant()
False
sage: (x^2).is_constant()
False
sage: (x^-2 + 2).is_constant()
False
sage: R(0).is_constant()
True
sage: R(42).is_constant()
True
sage: x.is_constant()
False
sage: (1/x).is_constant()
False

is_monomial()

Return True if self is a monomial; that is, if self is \(x^n\) for some integer \(n\).

EXAMPLES:

sage: k.<z> = LaurentPolynomialRing(QQ)
sage: z.is_monomial()
True
sage: k(1).is_monomial()
True
sage: (z+1).is_monomial()
False
sage: (z^-2909).is_monomial()
True
sage: (38*z^-2909).is_monomial()
False

is_square(root=False)

Return whether this Laurent polynomial is a square.

If root is set to True then return a pair made of the boolean answer together with None or a square root.

EXAMPLES:

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

sage: R.one().is_square()
True
sage: R(2).is_square()
False

sage: t.is_square()
False
sage: (t**-2).is_square()
True

Usage of the root option:

sage: p = (1 + t^-1 - 2*t^3)
sage: p.is_square(root=True)
(False, None)
sage: (p**2).is_square(root=True)
(True, -t^-1 - 1 + 2*t^3)

The answer is dependent of the base ring:

sage: # needs sage.rings.number_field
sage: S.<u> = LaurentPolynomialRing(QQbar)
sage: (2 + 4*t + 2*t^2).is_square()
False
sage: (2 + 4*u + 2*u^2).is_square()
True

is_unit()

Return True if this Laurent polynomial is a unit in this ring.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: (2 + t).is_unit()
False
sage: f = 2*t
sage: f.is_unit()
True
sage: 1/f
1/2*t^-1
sage: R(0).is_unit()
False
sage: R.<s> = LaurentPolynomialRing(ZZ)
sage: g = 2*s
sage: g.is_unit()
False
sage: 1/g
1/2*s^-1

ALGORITHM: A Laurent polynomial is a unit if and only if its “unit part” is a unit.

is_zero()

Return 1 if self is 0, else return 0.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: f = 1/x + x + x^2 + 3*x^4
sage: f.is_zero()
0
sage: z = 0*f
sage: z.is_zero()
1

number_of_terms()

Return the number of non-zero coefficients of self.

Also called weight, hamming weight or sparsity.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: f = x^3 - 1
sage: f.number_of_terms()
2
sage: R(0).number_of_terms()
0
sage: f = (x+1)^100
sage: f.number_of_terms()
101

The method hamming_weight() is an alias:

sage: f.hamming_weight()
101

polynomial_construction()

Return the polynomial and the shift in power used to construct the Laurent polynomial \(t^n u\).

OUTPUT:

A tuple (u, n) where u is the underlying polynomial and n is the power of the exponent shift.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: f = 1/x + x^2 + 3*x^4
sage: f.polynomial_construction()
(3*x^5 + x^3 + 1, -1)

quo_rem(other)

Divide self by other and return a quotient q and a remainder r such that self == q * other + r.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: (t^-3 - t^3).quo_rem(t^-1 - t)
(t^-2 + 1 + t^2, 0)
sage: (t^-2 + 3 + t).quo_rem(t^-4)
(t^2 + 3*t^4 + t^5, 0)

sage: num = t^-2 + t
sage: den = t^-2 + 1
sage: q, r = num.quo_rem(den)
sage: num == q * den + r
True

residue()

Return the residue of self.

The residue is the coefficient of \(t^-1\).

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ)
sage: f = 3*t^-2 - t^-1 + 3 + t^2
sage: f.residue()
-1
sage: g = -2*t^-2 + 4 + 3*t
sage: g.residue()
0
sage: f.residue().parent()
Rational Field

shift(k)

Return this Laurent polynomial multiplied by the power \(t^n\). Does not change this polynomial.

EXAMPLES:

sage: R.<t> = LaurentPolynomialRing(QQ['y'])
sage: f = (t+t^-1)^4; f
t^-4 + 4*t^-2 + 6 + 4*t^2 + t^4
sage: f.shift(10)
t^6 + 4*t^8 + 6*t^10 + 4*t^12 + t^14
sage: f >> 10
t^-14 + 4*t^-12 + 6*t^-10 + 4*t^-8 + t^-6
sage: f << 4
1 + 4*t^2 + 6*t^4 + 4*t^6 + t^8

truncate(n)

Return a polynomial with degree at most \(n-1\) whose \(j\)-th coefficients agree with self for all \(j < n\).

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: f = 1/x^12 + x^3 + x^5 + x^9
sage: f.truncate(10)
x^-12 + x^3 + x^5 + x^9
sage: f.truncate(5)
x^-12 + x^3
sage: f.truncate(-16)
0

valuation(p=None)

Return the valuation of self.

The valuation of a Laurent polynomial \(t^n u\) is \(n\) plus the valuation of \(u\).

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(ZZ)
sage: f = 1/x + x^2 + 3*x^4
sage: g = 1 - x + x^2 - x^4
sage: f.valuation()
-1
sage: g.valuation()
0

variable_name()

Return the name of variable of self as a string.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: f = 1/x + x^2 + 3*x^4
sage: f.variable_name()
'x'

variables()

Return the tuple of variables occurring in this Laurent polynomial.

EXAMPLES:

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: f = 1/x + x^2 + 3*x^4
sage: f.variables()
(x,)
sage: R.one().variables()
()