Ore modules

Let \(R\) be a commutative ring, \(\theta : K \to K\) by a ring endomorphism and \(\partial : K \to K\) be a \(\theta\)-derivation, that is an additive map satisfying the following axiom

\[\partial(x y) = \theta(x) \partial(y) + \partial(x) y\]

A Ore module over \((R, \theta, \partial)\) is a \(R\)-module \(M\) equipped with a additive \(f : M \to M\) such that

\[f(a x) = \theta(a) f(x) + \partial(a) x\]

Such a map \(f\) is called a pseudomorphism.

Equivalently, a Ore module is a module over the (noncommutative) Ore polynomial ring \(\mathcal S = R[X; \theta, \partial]\).

Defining Ore modules

SageMath provides support for creating and manipulating Ore modules that are finite free over the base ring \(R\).

To start with, the method sage.rings.polynomial.ore_polynomial_ring.OrePolynomialRing.quotient_module() creates the quotient \(\mathcal S/ \mathcal S P\), endowed with its structure of \(\mathcal S\)-module, that is its structure of Ore module:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^2 + z)
sage: M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + z)
>>> M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

Classical methods are available and we can work with elements in \(M\) as we do usually for vectors in finite free modules:

sage: M.basis()
[(1, 0), (0, 1)]

sage: v = M((z, z^2)); v
(z, z^2)
sage: z*v
(z^2, 2*z + 2)

>>> from sage.all import *
>>> M.basis()
[(1, 0), (0, 1)]

>>> v = M((z, z**Integer(2))); v
(z, z^2)
>>> z*v
(z^2, 2*z + 2)

The Ore action (or equivalently the structure of \(\mathcal S\)-module) is also easily accessible:

sage: X*v
(3*z^2 + 2*z, 2*z^2 + 4*z + 4)

>>> from sage.all import *
>>> X*v
(3*z^2 + 2*z, 2*z^2 + 4*z + 4)

The method sage.modules.ore_module.OreModule.pseudohom() returns the map \(f\) defining the action of \(X\):

sage: M.pseudohom()
Free module pseudomorphism (twisted by z |--> z^5) defined by the matrix
[  0   1]
[4*z   0]
Domain: Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
Codomain: Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> M.pseudohom()
Free module pseudomorphism (twisted by z |--> z^5) defined by the matrix
[  0   1]
[4*z   0]
Domain: Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
Codomain: Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

A useful feature is the possibility to give chosen names to the vectors of the canonical basis. This is easily done as follows:

sage: N.<u,v,w> = S.quotient_module(X^3 + z*X + 1)
sage: N
Ore module <u, v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: N.basis()
[u, v, w]

>>> from sage.all import *
>>> N = S.quotient_module(X**Integer(3) + z*X + Integer(1), names=('u', 'v', 'w',)); (u, v, w,) = N._first_ngens(3)
>>> N
Ore module <u, v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> N.basis()
[u, v, w]

Alternatively, one can pass in the argument names; this could be useful in particular when we want to name the vectors basis \(e_0, e_1, \ldots\):

sage: A = S.quotient_module(X^11 + z, names='e')
sage: A
Ore module <e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10> over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: A.basis()
[e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10]

>>> from sage.all import *
>>> A = S.quotient_module(X**Integer(11) + z, names='e')
>>> A
Ore module <e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10> over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> A.basis()
[e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10]

Do not forget to use the method inject_variables() to get the \(e_i\) in your namespace:

sage: e0
Traceback (most recent call last):
...
NameError: name 'e0' is not defined
sage: A.inject_variables()
Defining e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10
sage: e0
e0

>>> from sage.all import *
>>> e0
Traceback (most recent call last):
...
NameError: name 'e0' is not defined
>>> A.inject_variables()
Defining e0, e1, e2, e3, e4, e5, e6, e7, e8, e9, e10
>>> e0
e0

Submodules and quotients

SageMath provides facilities for creating submodules and quotient modules of Ore modules. First of all, we define the Ore module \(\mathcal S/\mathcal S P^2\) (for some Ore polynomials \(P\)), which is obviously not simple:

sage: P = X^2 + z*X + 1
sage: U = S.quotient_module(P^2, names='u')
sage: U.inject_variables()
Defining u0, u1, u2, u3

>>> from sage.all import *
>>> P = X**Integer(2) + z*X + Integer(1)
>>> U = S.quotient_module(P**Integer(2), names='u')
>>> U.inject_variables()
Defining u0, u1, u2, u3

We now build the submodule \(\mathcal S P / \mathcal S P^2\) using the method sage.modules.ore_module.OreModule.span():

sage: V = U.span(P*u0)
sage: V
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: V.basis()
[u0 + (z^2+2*z+2)*u2 + 4*z*u3,
 u1 + (2*z^2+4*z+4)*u2 + u3]

>>> from sage.all import *
>>> V = U.span(P*u0)
>>> V
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> V.basis()
[u0 + (z^2+2*z+2)*u2 + 4*z*u3,
 u1 + (2*z^2+4*z+4)*u2 + u3]

We underline that the span is really the \(\mathcal S\)-span and not the \(R\)-span (as otherwise, it will not be a Ore module).

As before, one can use the attributes names to give explicit names to the basis vectors:

sage: V = U.span(P*u0, names='v')
sage: V
Ore module <v0, v1> over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: V.inject_variables()
Defining v0, v1
sage: v0
v0
sage: U(v0)
u0 + (z^2+2*z+2)*u2 + 4*z*u3

>>> from sage.all import *
>>> V = U.span(P*u0, names='v')
>>> V
Ore module <v0, v1> over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> V.inject_variables()
Defining v0, v1
>>> v0
v0
>>> U(v0)
u0 + (z^2+2*z+2)*u2 + 4*z*u3

A coercion map from \(V\) to \(U\) is automatically created. Hence, we can safely combine vectors in \(V\) and vectors in \(U\) in a single expression:

sage: v0 - u0
(z^2+2*z+2)*u2 + 4*z*u3

>>> from sage.all import *
>>> v0 - u0
(z^2+2*z+2)*u2 + 4*z*u3

We can create the quotient \(U/V\) using a similar syntax:

sage: W = U.quo(P*u0)
sage: W
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: W.basis()
[u2, u3]

>>> from sage.all import *
>>> W = U.quo(P*u0)
>>> W
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> W.basis()
[u2, u3]

We see that SageMath reuses by default the names of the representatives to denote the vectors in the quotient \(U/V\). This behaviour can be overridden by providing explicit names using the attributes names.

Shortcuts for creating quotients are also available:

sage: U / (P*u0)
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: U/V
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> U / (P*u0)
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> U/V
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

Morphisms of Ore modules

For a tutorial on morphisms of Ore modules, we refer to sage.modules.ore_module_morphism.

AUTHOR:

  • Xavier Caruso (2024-10)

class sage.modules.ore_module.OreAction[source]

Bases: Action

Action by left multiplication of Ore polynomial rings over Ore modules.

class sage.modules.ore_module.OreModule(mat, ore, names, category)[source]

Bases: UniqueRepresentation, FreeModule_ambient

Generic class for Ore modules.

Element[source]

alias of OreModuleElement

an_element()[source]

Return an element of this Ore module.

EXAMPLES:

When the Ore module is not zero, the returned element is the first vector of the distinguished basis:

sage: K.<t> = Frac(QQ['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: M.<u,v> = S.quotient_module(X^2 - t)
sage: M.an_element()
u

>>> from sage.all import *
>>> K = Frac(QQ['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) - t, names=('u', 'v',)); (u, v,) = M._first_ngens(2)
>>> M.an_element()
u

On the contrary, when the Ore module vanishes, the returned element is of course zero:

sage: N = M / u
sage: N
Ore module of rank 0 over Fraction Field of Univariate Polynomial Ring in t over Rational Field twisted by d/dt
sage: N.an_element()
0

>>> from sage.all import *
>>> N = M / u
>>> N
Ore module of rank 0 over Fraction Field of Univariate Polynomial Ring in t over Rational Field twisted by d/dt
>>> N.an_element()
0
basis()[source]

Return the canonical basis of this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^3 - z)
sage: M.basis()
[(1, 0, 0), (0, 1, 0), (0, 0, 1)]

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(3) - z)
>>> M.basis()
[(1, 0, 0), (0, 1, 0), (0, 0, 1)]
gen(i)[source]

Return the \(i\)-th vector of the canonical basis of this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^3 - z)
sage: M.gen(0)
(1, 0, 0)
sage: M.gen(1)
(0, 1, 0)
sage: M.gen(2)
(0, 0, 1)
sage: M.gen(3)
Traceback (most recent call last):
...
IndexError: generator is not defined

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(3) - z)
>>> M.gen(Integer(0))
(1, 0, 0)
>>> M.gen(Integer(1))
(0, 1, 0)
>>> M.gen(Integer(2))
(0, 0, 1)
>>> M.gen(Integer(3))
Traceback (most recent call last):
...
IndexError: generator is not defined
gens()[source]

Return the canonical basis of this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^3 - z)
sage: M.gens()
[(1, 0, 0), (0, 1, 0), (0, 0, 1)]

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(3) - z)
>>> M.gens()
[(1, 0, 0), (0, 1, 0), (0, 0, 1)]
hom(im_gens, codomain=None)[source]

Return the morphism from this Ore module to codomain defined by im_gens.

INPUT:

  • im_gens – a datum defining the morphism to build; it could either a list, a tuple, a dictionary or a morphism of Ore modules

  • codomain (default: None) – a Ore module, the codomain of the morphism; if None, it is inferred from im_gens

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X^3 + 2*t*X^2 + (t^2 + 2)*X + t
sage: Q = t*X^2 - X + 1

sage: U = S.quotient_module(P, names='u')
sage: U.inject_variables()
Defining u0, u1, u2
sage: V = S.quotient_module(P*Q, names='v')
sage: V.inject_variables()
Defining v0, v1, v2, v3, v4

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(3) + Integer(2)*t*X**Integer(2) + (t**Integer(2) + Integer(2))*X + t
>>> Q = t*X**Integer(2) - X + Integer(1)

>>> U = S.quotient_module(P, names='u')
>>> U.inject_variables()
Defining u0, u1, u2
>>> V = S.quotient_module(P*Q, names='v')
>>> V.inject_variables()
Defining v0, v1, v2, v3, v4

The first method for creating a morphism from \(U\) to \(V\) is to explicitly write down its matrix in the canonical bases:

sage: mat = matrix(3, 5, [1, 4, t, 0, 0,
....:                     0, 1, 0, t, 0,
....:                     0, 0, 1, 1, t])
sage: f = U.hom(mat, codomain=V)
sage: f
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> mat = matrix(Integer(3), Integer(5), [Integer(1), Integer(4), t, Integer(0), Integer(0),
...                     Integer(0), Integer(1), Integer(0), t, Integer(0),
...                     Integer(0), Integer(0), Integer(1), Integer(1), t])
>>> f = U.hom(mat, codomain=V)
>>> f
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

This method is however not really convenient because it requires to compute beforehand all the entries of the defining matrix. Instead, we can pass the list of images of the generators:

sage: g = U.hom([Q*v0, X*Q*v0, X^2*Q*v0])
sage: g
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: g.matrix()
[1 4 t 0 0]
[0 1 0 t 0]
[0 0 1 1 t]

>>> from sage.all import *
>>> g = U.hom([Q*v0, X*Q*v0, X**Integer(2)*Q*v0])
>>> g
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> g.matrix()
[1 4 t 0 0]
[0 1 0 t 0]
[0 0 1 1 t]

One can even give the values of the morphism on a smaller set as soon as the latter generates the domain as Ore module. The syntax uses dictionaries as follows:

sage: h = U.hom({u0: Q*v0})
sage: h
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: g == h
True

>>> from sage.all import *
>>> h = U.hom({u0: Q*v0})
>>> h
Ore module morphism:
  From: Ore module <u0, u1, u2> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> g == h
True

Finally im_gens can also be itself a Ore morphism, in which case SageMath tries to cast it into a morphism with the requested domains and codomains. As an example below, we restrict \(g\) to a subspace:

sage: C.<c0,c1> = U.span((X + t)*u0)
sage: gC = C.hom(g)
sage: gC
Ore module morphism:
  From: Ore module <c0, c1> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

sage: g(c0) == gC(c0)
True
sage: g(c1) == gC(c1)
True

>>> from sage.all import *
>>> C = U.span((X + t)*u0, names=('c0', 'c1',)); (c0, c1,) = C._first_ngens(2)
>>> gC = C.hom(g)
>>> gC
Ore module morphism:
  From: Ore module <c0, c1> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v0, v1, v2, v3, v4> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> g(c0) == gC(c0)
True
>>> g(c1) == gC(c1)
True
identity_morphism()[source]

Return the identity morphism of this Ore module.

EXAMPLES:

sage: K.<a> = GF(7^5)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M.<u,v> = S.quotient_module(X^2 + a*X + a^2)
sage: id = M.identity_morphism()
sage: id
Ore module endomorphism of Ore module <u, v> over Finite Field in a of size 7^5 twisted by a |--> a^7

sage: id(u)
u
sage: id(v)
v

>>> from sage.all import *
>>> K = GF(Integer(7)**Integer(5), names=('a',)); (a,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + a*X + a**Integer(2), names=('u', 'v',)); (u, v,) = M._first_ngens(2)
>>> id = M.identity_morphism()
>>> id
Ore module endomorphism of Ore module <u, v> over Finite Field in a of size 7^5 twisted by a |--> a^7

>>> id(u)
u
>>> id(v)
v
is_zero()[source]

Return True if this Ore module is reduced to zero.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^2 + z)
sage: M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: M.is_zero()
False

sage: Q = M.quo(M)
sage: Q.is_zero()
True

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + z)
>>> M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> M.is_zero()
False

>>> Q = M.quo(M)
>>> Q.is_zero()
True
matrix()[source]

Return the matrix giving the action of the Ore variable on this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: P = X^3 + z*X^2 - z^2*X + (z+2)
sage: M = S.quotient_module(P)
sage: M.matrix()
[      0       1       0]
[      0       0       1]
[4*z + 3     z^2     4*z]

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(3) + z*X**Integer(2) - z**Integer(2)*X + (z+Integer(2))
>>> M = S.quotient_module(P)
>>> M.matrix()
[      0       1       0]
[      0       0       1]
[4*z + 3     z^2     4*z]

We recognize the companion matrix attached to the Ore polynomial \(P\). This is of course not a coincidence given that the pseudomorphism corresponds to the left multiplication

See also

pseudohom()

module()[source]

Return the underlying free module of this Ore module.

EXAMPLES:

sage: A.<t> = QQ['t']
sage: S.<X> = OrePolynomialRing(A, A.derivation())
sage: M = S.quotient_module(X^3 - t)
sage: M
Ore module of rank 3 over Univariate Polynomial Ring in t over Rational Field twisted by d/dt

sage: M.module()
Ambient free module of rank 3 over the principal ideal domain Univariate Polynomial Ring in t over Rational Field

>>> from sage.all import *
>>> A = QQ['t']; (t,) = A._first_ngens(1)
>>> S = OrePolynomialRing(A, A.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(3) - t)
>>> M
Ore module of rank 3 over Univariate Polynomial Ring in t over Rational Field twisted by d/dt

>>> M.module()
Ambient free module of rank 3 over the principal ideal domain Univariate Polynomial Ring in t over Rational Field
multiplication_map(P)[source]

Return the multiplication by \(P\) acting on this Ore module.

INPUT:

  • P – a scalar in the base ring, or a Ore polynomial

EXAMPLES:

sage: K.<a> = GF(7^5)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: P = X^3 + a*X^2 + X - a^2
sage: M = S.quotient_module(P)

>>> from sage.all import *
>>> K = GF(Integer(7)**Integer(5), names=('a',)); (a,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(3) + a*X**Integer(2) + X - a**Integer(2)
>>> M = S.quotient_module(P)

We define the scalar multiplication by an element in the base ring:

sage: f = M.multiplication_map(3)
sage: f
Ore module endomorphism of Ore module of rank 3 over Finite Field in a of size 7^5 twisted by a |--> a^7
sage: f.matrix()
[3 0 0]
[0 3 0]
[0 0 3]

>>> from sage.all import *
>>> f = M.multiplication_map(Integer(3))
>>> f
Ore module endomorphism of Ore module of rank 3 over Finite Field in a of size 7^5 twisted by a |--> a^7
>>> f.matrix()
[3 0 0]
[0 3 0]
[0 0 3]

Be careful that an element in the base ring defines a Ore morphism if and only if it is fixed by the twisting morphisms and killed by the derivation (otherwise the multiplication by this element does not commute with the Ore action). In SageMath, attempting to create the multiplication by an element which does not fulfill these requirements leads to an error:

sage: M.multiplication_map(a)
Traceback (most recent call last):
...
ValueError: does not define a morphism of Ore modules

>>> from sage.all import *
>>> M.multiplication_map(a)
Traceback (most recent call last):
...
ValueError: does not define a morphism of Ore modules

As soon as it defines a Ore morphism, one can also build the left multiplication by an Ore polynomial:

sage: g = M.multiplication_map(X^5)
sage: g
Ore module endomorphism of Ore module of rank 3 over Finite Field in a of size 7^5 twisted by a |--> a^7
sage: g.matrix()
[    3*a^4 + 3*a^3 + 6*a^2 + 5*a       4*a^4 + 5*a^3 + 2*a^2 + 6         6*a^4 + 6*a^3 + a^2 + 4]
[                        a^2 + 3 5*a^4 + 5*a^3 + 6*a^2 + 4*a + 1                 a^3 + 5*a^2 + 4]
[6*a^4 + 6*a^3 + 3*a^2 + 3*a + 1         4*a^4 + 2*a^3 + 3*a + 5 6*a^4 + 6*a^3 + 2*a^2 + 5*a + 2]

>>> from sage.all import *
>>> g = M.multiplication_map(X**Integer(5))
>>> g
Ore module endomorphism of Ore module of rank 3 over Finite Field in a of size 7^5 twisted by a |--> a^7
>>> g.matrix()
[    3*a^4 + 3*a^3 + 6*a^2 + 5*a       4*a^4 + 5*a^3 + 2*a^2 + 6         6*a^4 + 6*a^3 + a^2 + 4]
[                        a^2 + 3 5*a^4 + 5*a^3 + 6*a^2 + 4*a + 1                 a^3 + 5*a^2 + 4]
[6*a^4 + 6*a^3 + 3*a^2 + 3*a + 1         4*a^4 + 2*a^3 + 3*a + 5 6*a^4 + 6*a^3 + 2*a^2 + 5*a + 2]

We check that the characteristic polynomial of \(g\) is the reduced norm of the Ore polynomial \(P\) we started with (this is a classical property):

sage: g.charpoly()
x^3 + 4*x^2 + 2*x + 5
sage: P.reduced_norm(var='x')
x^3 + 4*x^2 + 2*x + 5

>>> from sage.all import *
>>> g.charpoly()
x^3 + 4*x^2 + 2*x + 5
>>> P.reduced_norm(var='x')
x^3 + 4*x^2 + 2*x + 5
ore_ring(names='x', action=True)[source]

Return the underlying Ore polynomial ring.

INPUT:

  • names (default: x) – a string, the name of the variable

  • action (default: True) – a boolean; if True, an action of the Ore polynomial ring on the Ore module is set

EXAMPLES:

sage: K.<a> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M.<e1,e2> = S.quotient_module(X^2 - a)
sage: M.ore_ring()
Ore Polynomial Ring in x over Finite Field in a of size 5^3 twisted by a |--> a^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('a',)); (a,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) - a, names=('e1', 'e2',)); (e1, e2,) = M._first_ngens(2)
>>> M.ore_ring()
Ore Polynomial Ring in x over Finite Field in a of size 5^3 twisted by a |--> a^5

We can use a different variable name:

sage: M.ore_ring('Y')
Ore Polynomial Ring in Y over Finite Field in a of size 5^3 twisted by a |--> a^5

>>> from sage.all import *
>>> M.ore_ring('Y')
Ore Polynomial Ring in Y over Finite Field in a of size 5^3 twisted by a |--> a^5

Alternatively, one can use the following shortcut:

sage: T.<Z> = M.ore_ring()
sage: T
Ore Polynomial Ring in Z over Finite Field in a of size 5^3 twisted by a |--> a^5

>>> from sage.all import *
>>> T = M.ore_ring(names=('Z',)); (Z,) = T._first_ngens(1)
>>> T
Ore Polynomial Ring in Z over Finite Field in a of size 5^3 twisted by a |--> a^5

In all the above cases, an action of the returned Ore polynomial ring on \(M\) is registered:

sage: Z*e1
e2
sage: Z*e2
a*e1

>>> from sage.all import *
>>> Z*e1
e2
>>> Z*e2
a*e1

Specifying action=False prevents this to happen:

sage: T.<U> = M.ore_ring(action=False)
sage: U*e1
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for *:
    'Ore Polynomial Ring in U over Finite Field in a of size 5^3 twisted by a |--> a^5' and
    'Ore module <e1, e2> over Finite Field in a of size 5^3 twisted by a |--> a^5'

>>> from sage.all import *
>>> T = M.ore_ring(action=False, names=('U',)); (U,) = T._first_ngens(1)
>>> U*e1
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for *:
    'Ore Polynomial Ring in U over Finite Field in a of size 5^3 twisted by a |--> a^5' and
    'Ore module <e1, e2> over Finite Field in a of size 5^3 twisted by a |--> a^5'
pseudohom()[source]

Return the pseudomorphism giving the action of the Ore variable on this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: P = X^3 + z*X^2 - z^2*X + (z+2)
sage: M = S.quotient_module(P)
sage: M.pseudohom()
Free module pseudomorphism (twisted by z |--> z^5) defined by the matrix
[      0       1       0]
[      0       0       1]
[4*z + 3     z^2     4*z]
Domain: Ore module of rank 3 over Finite Field in z of size 5^3 twisted by z |--> z^5
Codomain: Ore module of rank 3 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(3) + z*X**Integer(2) - z**Integer(2)*X + (z+Integer(2))
>>> M = S.quotient_module(P)
>>> M.pseudohom()
Free module pseudomorphism (twisted by z |--> z^5) defined by the matrix
[      0       1       0]
[      0       0       1]
[4*z + 3     z^2     4*z]
Domain: Ore module of rank 3 over Finite Field in z of size 5^3 twisted by z |--> z^5
Codomain: Ore module of rank 3 over Finite Field in z of size 5^3 twisted by z |--> z^5

See also

matrix()

quo(sub, names=None, check=True)[source]

Return the quotient of this Ore module by the submodule generated (over the underlying Ore ring) by gens.

INPUT:

  • gens – a list of vectors or submodules of this Ore module

  • names (default: None) – the name of the vectors in a basis of the quotient

  • check (default: True) – a boolean, ignored

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X^2 + t*X + 1
sage: M = S.quotient_module(P^3, names='e')
sage: M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(2) + t*X + Integer(1)
>>> M = S.quotient_module(P**Integer(3), names='e')
>>> M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

We create the quotient \(M/MP\):

sage: modP = M.quotient(P*e0)
sage: modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> modP = M.quotient(P*e0)
>>> modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

As a shortcut, we can write quo instead of quotient or even use the / operator:

sage: modP = M / (P*e0)
sage: modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> modP = M / (P*e0)
>>> modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

By default, the vectors in the quotient have the same names as their representatives in \(M\):

sage: modP.basis()
[e4, e5]

>>> from sage.all import *
>>> modP.basis()
[e4, e5]

One can override this behavior by setting the attributes names:

sage: modP = M.quo(P*e0, names='u')
sage: modP.inject_variables()
Defining u0, u1
sage: modP.basis()
[u0, u1]

>>> from sage.all import *
>>> modP = M.quo(P*e0, names='u')
>>> modP.inject_variables()
Defining u0, u1
>>> modP.basis()
[u0, u1]

Note that a coercion map from the initial Ore module to its quotient is automatically set. As a consequence, combining elements of M and modP in the same formula works:

sage: t*u0 + e1
(t^3+4*t)*u0 + (t^2+2)*u1

>>> from sage.all import *
>>> t*u0 + e1
(t^3+4*t)*u0 + (t^2+2)*u1

One can combine the construction of quotients and submodules without trouble. For instance, here we build the space \(M P / M P^2\):

sage: modP2 = M / (P^2*e0)
sage: N = modP2.span(P*e0)
sage: N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: N.basis()
[e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

>>> from sage.all import *
>>> modP2 = M / (P**Integer(2)*e0)
>>> N = modP2.span(P*e0)
>>> N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> N.basis()
[e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

See also

quo(), span()

quotient(sub, names=None, check=True)[source]

Return the quotient of this Ore module by the submodule generated (over the underlying Ore ring) by gens.

INPUT:

  • gens – a list of vectors or submodules of this Ore module

  • names (default: None) – the name of the vectors in a basis of the quotient

  • check (default: True) – a boolean, ignored

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X^2 + t*X + 1
sage: M = S.quotient_module(P^3, names='e')
sage: M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(2) + t*X + Integer(1)
>>> M = S.quotient_module(P**Integer(3), names='e')
>>> M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

We create the quotient \(M/MP\):

sage: modP = M.quotient(P*e0)
sage: modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> modP = M.quotient(P*e0)
>>> modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

As a shortcut, we can write quo instead of quotient or even use the / operator:

sage: modP = M / (P*e0)
sage: modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> modP = M / (P*e0)
>>> modP
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

By default, the vectors in the quotient have the same names as their representatives in \(M\):

sage: modP.basis()
[e4, e5]

>>> from sage.all import *
>>> modP.basis()
[e4, e5]

One can override this behavior by setting the attributes names:

sage: modP = M.quo(P*e0, names='u')
sage: modP.inject_variables()
Defining u0, u1
sage: modP.basis()
[u0, u1]

>>> from sage.all import *
>>> modP = M.quo(P*e0, names='u')
>>> modP.inject_variables()
Defining u0, u1
>>> modP.basis()
[u0, u1]

Note that a coercion map from the initial Ore module to its quotient is automatically set. As a consequence, combining elements of M and modP in the same formula works:

sage: t*u0 + e1
(t^3+4*t)*u0 + (t^2+2)*u1

>>> from sage.all import *
>>> t*u0 + e1
(t^3+4*t)*u0 + (t^2+2)*u1

One can combine the construction of quotients and submodules without trouble. For instance, here we build the space \(M P / M P^2\):

sage: modP2 = M / (P^2*e0)
sage: N = modP2.span(P*e0)
sage: N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: N.basis()
[e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

>>> from sage.all import *
>>> modP2 = M / (P**Integer(2)*e0)
>>> N = modP2.span(P*e0)
>>> N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> N.basis()
[e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

See also

quo(), span()

random_element(*args, **kwds)[source]

Return a random element in this Ore module.

Extra arguments are passed to the random generator of the base ring.

EXAMPLES:

sage: A.<t> = QQ['t']
sage: S.<X> = OrePolynomialRing(A, A.derivation())
sage: M = S.quotient_module(X^3 - t, names='e')
sage: M.random_element()   # random
(-1/2*t^2 - 3/4*t + 3/2)*e0 + (-3/2*t^2 - 3*t + 4)*e1 + (-6*t + 2)*e2

sage: M.random_element(degree=5)   # random
(4*t^5 - 1/2*t^4 + 3/2*t^3 + 6*t^2 - t - 1/10)*e0 + (19/3*t^5 - t^3 - t^2 + 1)*e1 + (t^5 + 4*t^4 + 4*t^2 + 1/3*t - 33)*e2

>>> from sage.all import *
>>> A = QQ['t']; (t,) = A._first_ngens(1)
>>> S = OrePolynomialRing(A, A.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(3) - t, names='e')
>>> M.random_element()   # random
(-1/2*t^2 - 3/4*t + 3/2)*e0 + (-3/2*t^2 - 3*t + 4)*e1 + (-6*t + 2)*e2

>>> M.random_element(degree=Integer(5))   # random
(4*t^5 - 1/2*t^4 + 3/2*t^3 + 6*t^2 - t - 1/10)*e0 + (19/3*t^5 - t^3 - t^2 + 1)*e1 + (t^5 + 4*t^4 + 4*t^2 + 1/3*t - 33)*e2
rename_basis(names, coerce=False)[source]

Return the same Ore module with the given naming for the vectors in its distinguished basis.

INPUT:

  • names – a string or a list of strings, the new names

  • coerce (default: False) – a boolean; if True, a coercion map from this Ore module to renamed version is set

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^2 + z)
sage: M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

sage: Me = M.rename_basis('e')
sage: Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + z)
>>> M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> Me = M.rename_basis('e')
>>> Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

Now compare how elements are displayed:

sage: M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
sage: Me.random_element()  # random
(2*z+4)*e0 + (z^2+4*z+4)*e1

>>> from sage.all import *
>>> M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
>>> Me.random_element()  # random
(2*z+4)*e0 + (z^2+4*z+4)*e1

At this point, there is no coercion map between M and Me. Therefore, adding elements in both parents results in an error:

sage: M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

>>> from sage.all import *
>>> M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

In order to set this coercion, one should define Me by passing the extra argument coerce=True:

sage: Me = M.rename_basis('e', coerce=True)
sage: M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2+z+4)*e1

>>> from sage.all import *
>>> Me = M.rename_basis('e', coerce=True)
>>> M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2+z+4)*e1

Warning

Use coerce=True with extreme caution. Indeed, setting inappropriate coercion maps may result in a circular path in the coercion graph which, in turn, could eventually break the coercion system.

Note that the bracket construction also works:

sage: M.<v,w> = M.rename_basis()
sage: M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> M = M.rename_basis(names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

In this case, \(v\) and \(w\) are automatically defined:

sage: v + w
v + w

>>> from sage.all import *
>>> v + w
v + w
span(gens, names=None)[source]

Return the submodule of this Ore module generated (over the underlying Ore ring) by gens.

INPUT:

  • gens – a list of vectors or submodules of this Ore module

  • names (default: None) – the name of the vectors in a basis of this submodule

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X^2 + t*X + 1
sage: M = S.quotient_module(P^3, names='e')
sage: M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X**Integer(2) + t*X + Integer(1)
>>> M = S.quotient_module(P**Integer(3), names='e')
>>> M.inject_variables()
Defining e0, e1, e2, e3, e4, e5

We create the submodule \(M P\):

sage: MP = M.span([P*e0])
sage: MP
Ore module of rank 4 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: MP.basis()
[e0 + (t^4+t^2+3)*e4 + t^3*e5,
 e1 + (4*t^3+2*t)*e4 + (4*t^2+3)*e5,
 e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

>>> from sage.all import *
>>> MP = M.span([P*e0])
>>> MP
Ore module of rank 4 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> MP.basis()
[e0 + (t^4+t^2+3)*e4 + t^3*e5,
 e1 + (4*t^3+2*t)*e4 + (4*t^2+3)*e5,
 e2 + (2*t^2+2)*e4 + 2*t*e5,
 e3 + 4*t*e4 + 4*e5]

When there is only one generator, encapsulating it in a list is not necessary; one can equally write:

sage: MP = M.span(P*e0)

>>> from sage.all import *
>>> MP = M.span(P*e0)

If one wants, one can give names to the basis of the submodule using the attribute names:

sage: MP2 = M.span(P^2*e0, names='u')
sage: MP2.inject_variables()
Defining u0, u1
sage: MP2.basis()
[u0, u1]

sage: M(u0)
e0 + (t^2+4)*e2 + 3*t^3*e3 + (t^2+1)*e4 + 3*t*e5

>>> from sage.all import *
>>> MP2 = M.span(P**Integer(2)*e0, names='u')
>>> MP2.inject_variables()
Defining u0, u1
>>> MP2.basis()
[u0, u1]

>>> M(u0)
e0 + (t^2+4)*e2 + 3*t^3*e3 + (t^2+1)*e4 + 3*t*e5

Note that a coercion map from the submodule to the ambient module is automatically set:

sage: M.has_coerce_map_from(MP2)
True

>>> from sage.all import *
>>> M.has_coerce_map_from(MP2)
True

Therefore, combining elements of M and MP2 in the same expression perfectly works:

sage: t*u0 + e1
t*e0 + e1 + (t^3+4*t)*e2 + 3*t^4*e3 + (t^3+t)*e4 + 3*t^2*e5

>>> from sage.all import *
>>> t*u0 + e1
t*e0 + e1 + (t^3+4*t)*e2 + 3*t^4*e3 + (t^3+t)*e4 + 3*t^2*e5

Here is an example with multiple generators:

sage: MM = M.span([MP2, P*e1])
sage: MM.basis()
[e0, e1, e2, e3, e4, e5]

>>> from sage.all import *
>>> MM = M.span([MP2, P*e1])
>>> MM.basis()
[e0, e1, e2, e3, e4, e5]

In this case, we obtain the whole space.

Creating submodules of submodules is also allowed:

sage: N = MP.span(P^2*e0)
sage: N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: N.basis()
[e0 + (t^2+4)*e2 + 3*t^3*e3 + (t^2+1)*e4 + 3*t*e5,
 e1 + (4*t^2+4)*e3 + 3*t*e4 + 4*e5]

>>> from sage.all import *
>>> N = MP.span(P**Integer(2)*e0)
>>> N
Ore module of rank 2 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> N.basis()
[e0 + (t^2+4)*e2 + 3*t^3*e3 + (t^2+1)*e4 + 3*t*e5,
 e1 + (4*t^2+4)*e3 + 3*t*e4 + 4*e5]

See also

quotient()

twisting_derivation()[source]

Return the twisting derivation corresponding to this Ore module.

EXAMPLES:

sage: R.<t> = QQ[]
sage: T.<Y> = OrePolynomialRing(R, R.derivation())
sage: M = T.quotient_module(Y + t^2)
sage: M.twisting_derivation()
d/dt

>>> from sage.all import *
>>> R = QQ['t']; (t,) = R._first_ngens(1)
>>> T = OrePolynomialRing(R, R.derivation(), names=('Y',)); (Y,) = T._first_ngens(1)
>>> M = T.quotient_module(Y + t**Integer(2))
>>> M.twisting_derivation()
d/dt

When the twisting derivation in zero, nothing is returned:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X + z)
sage: M.twisting_derivation()

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X + z)
>>> M.twisting_derivation()

See also

twisting_morphism()

twisting_morphism()[source]

Return the twisting morphism corresponding to this Ore module.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X + z)
sage: M.twisting_morphism()
Frobenius endomorphism z |--> z^5 on Finite Field in z of size 5^3

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X + z)
>>> M.twisting_morphism()
Frobenius endomorphism z |--> z^5 on Finite Field in z of size 5^3

When the twisting morphism is trivial (that is, the identity), nothing is returned:

sage: R.<t> = QQ[]
sage: T.<Y> = OrePolynomialRing(R, R.derivation())
sage: M = T.quotient_module(Y + t^2)
sage: M.twisting_morphism()

>>> from sage.all import *
>>> R = QQ['t']; (t,) = R._first_ngens(1)
>>> T = OrePolynomialRing(R, R.derivation(), names=('Y',)); (Y,) = T._first_ngens(1)
>>> M = T.quotient_module(Y + t**Integer(2))
>>> M.twisting_morphism()

See also

twisting_derivation()

class sage.modules.ore_module.OreQuotientModule(cover, basis, names)[source]

Bases: OreModule

Class for quotients of Ore modules.

cover()[source]

If this quotient in \(M/N\), return \(M\).

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: M.<v,w> = S.quotient_module((X + t)^2)
sage: N = M.quo((X + t)*v)

sage: N.cover()
Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: N.cover() is M
True

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + t)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> N = M.quo((X + t)*v)

>>> N.cover()
Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> N.cover() is M
True

See also

relations()

morphism_modulo(f)[source]

If this quotient in \(M/N\) and \(f : X \to M\) is a morphism, return the induced map \(X \to M/N\).

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X + t
sage: M.<v,w> = S.quotient_module(P^2)
sage: Q.<wbar> = M.quo(P*v)

sage: f = M.multiplication_map(X^5)
sage: f
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: g = Q.morphism_modulo(f)
sage: g
Ore module morphism:
  From: Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <wbar> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X + t
>>> M = S.quotient_module(P**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> Q = M.quo(P*v, names=('wbar',)); (wbar,) = Q._first_ngens(1)

>>> f = M.multiplication_map(X**Integer(5))
>>> f
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> g = Q.morphism_modulo(f)
>>> g
Ore module morphism:
  From: Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <wbar> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
morphism_quotient(f)[source]

If this quotient in \(M/N\) and \(f : M \to X\) is a morphism vanishing on \(N\), return the induced map \(M/N \to X\).

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: P = X + t
sage: M.<v,w> = S.quotient_module(P^2)
sage: Q.<wbar> = M.quo(P*v)

sage: f = M.hom({v: P*v})
sage: f
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: g = Q.morphism_quotient(f)
sage: g
Ore module morphism:
  From: Ore module <wbar> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X + t
>>> M = S.quotient_module(P**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> Q = M.quo(P*v, names=('wbar',)); (wbar,) = Q._first_ngens(1)

>>> f = M.hom({v: P*v})
>>> f
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> g = Q.morphism_quotient(f)
>>> g
Ore module morphism:
  From: Ore module <wbar> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

When the given morphism does not vanish on \(N\), an error is raised:

sage: h = M.multiplication_map(X^5)
sage: h
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: Q.morphism_quotient(h)
Traceback (most recent call last):
...
ValueError: the morphism does not factor through this quotient

>>> from sage.all import *
>>> h = M.multiplication_map(X**Integer(5))
>>> h
Ore module endomorphism of Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> Q.morphism_quotient(h)
Traceback (most recent call last):
...
ValueError: the morphism does not factor through this quotient
projection_morphism()[source]

Return the projection from the cover module to this quotient.

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: M.<v,w> = S.quotient_module((X + t)^2)
sage: Q = M.quo((X + t)*v)
sage: Q.projection_morphism()
Ore module morphism:
  From: Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module of rank 1 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + t)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> Q = M.quo((X + t)*v)
>>> Q.projection_morphism()
Ore module morphism:
  From: Ore module <v, w> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
  To:   Ore module of rank 1 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
relations(names=None)[source]

If this quotient in \(M/N\), return \(N\).

INPUT:

  • names – the names of the vectors of the basis of \(N\), or None

EXAMPLES:

sage: K.<t> = Frac(GF(5)['t'])
sage: S.<X> = OrePolynomialRing(K, K.derivation())
sage: M.<v,w> = S.quotient_module((X + t)^2)
sage: Q = M.quo((X + t)*v)

sage: N = Q.relations()
sage: N
Ore module of rank 1 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: (X + t)*v in N
True
sage: Q == M/N
True

>>> from sage.all import *
>>> K = Frac(GF(Integer(5))['t'], names=('t',)); (t,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.derivation(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + t)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> Q = M.quo((X + t)*v)

>>> N = Q.relations()
>>> N
Ore module of rank 1 over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> (X + t)*v in N
True
>>> Q == M/N
True

It is also possible to define names for the basis elements of \(N\):

sage: N.<u> = Q.relations()
sage: N
Ore module <u> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
sage: M(u)
v + 1/t*w

>>> from sage.all import *
>>> N = Q.relations(names=('u',)); (u,) = N._first_ngens(1)
>>> N
Ore module <u> over Fraction Field of Univariate Polynomial Ring in t over Finite Field of size 5 twisted by d/dt
>>> M(u)
v + 1/t*w

See also

relations()

rename_basis(names, coerce=False)[source]

Return the same Ore module with the given naming for the vectors in its distinguished basis.

INPUT:

  • names – a string or a list of strings, the new names

  • coerce (default: False) – a boolean; if True, a coercion map from this Ore module to the renamed version is set

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^2 + z*X + 1)
sage: M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

sage: Me = M.rename_basis('e')
sage: Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + z*X + Integer(1))
>>> M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> Me = M.rename_basis('e')
>>> Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

Now compare how elements are displayed:

sage: M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
sage: Me.random_element()  # random
(2*z + 4)*e0 + (z^2 + 4*z + 4)*e1

>>> from sage.all import *
>>> M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
>>> Me.random_element()  # random
(2*z + 4)*e0 + (z^2 + 4*z + 4)*e1

At this point, there is no coercion map between M and Me. Therefore, adding elements in both parents results in an error:

sage: M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

>>> from sage.all import *
>>> M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

In order to set this coercion, one should define Me by passing the extra argument coerce=True:

sage: Me = M.rename_basis('e', coerce=True)
sage: M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2 + z + 4)*e1

>>> from sage.all import *
>>> Me = M.rename_basis('e', coerce=True)
>>> M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2 + z + 4)*e1

Warning

Use coerce=True with extreme caution. Indeed, setting inappropriate coercion maps may result in a circular path in the coercion graph which, in turn, could eventually break the coercion system.

Note that the bracket construction also works:

sage: M.<v,w> = M.rename_basis()
sage: M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> M = M.rename_basis(names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

In this case, \(v\) and \(w\) are automatically defined:

sage: v + w
v + w

>>> from sage.all import *
>>> v + w
v + w
class sage.modules.ore_module.OreSubmodule(ambient, basis, names)[source]

Bases: OreModule

Class for submodules of Ore modules.

ambient()[source]

Return the ambient Ore module in which this submodule lives.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M.<v,w> = S.quotient_module((X + z)^2)
sage: N = M.span((X + z)*v)
sage: N.ambient()
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: N.ambient() is M
True

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + z)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> N = M.span((X + z)*v)
>>> N.ambient()
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> N.ambient() is M
True
injection_morphism()[source]

Return the inclusion of this submodule in the ambient space.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M.<v,w> = S.quotient_module((X + z)^2)
sage: N = M.span((X + z)*v)
sage: N.injection_morphism()
Ore module morphism:
  From: Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + z)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> N = M.span((X + z)*v)
>>> N.injection_morphism()
Ore module morphism:
  From: Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
morphism_corestriction(f)[source]

If the image of \(f\) is contained in this submodule, return the corresponding corestriction of \(f\).

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: P = X + z
sage: M.<v,w> = S.quotient_module(P^2)
sage: N = M.span(P*v)

sage: f = M.hom({v: P*v})
sage: f
Ore module endomorphism of Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

sage: g = N.morphism_corestriction(f)
sage: g
Ore module morphism:
  From: Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: g.matrix()
[    z]
[4*z^2]

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> P = X + z
>>> M = S.quotient_module(P**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> N = M.span(P*v)

>>> f = M.hom({v: P*v})
>>> f
Ore module endomorphism of Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> g = N.morphism_corestriction(f)
>>> g
Ore module morphism:
  From: Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> g.matrix()
[    z]
[4*z^2]

When the image of the morphism is not contained in this submodule, an error is raised:

sage: h = M.multiplication_map(X^3)
sage: N.morphism_corestriction(h)
Traceback (most recent call last):
...
ValueError: the image of the morphism is not contained in this submodule

>>> from sage.all import *
>>> h = M.multiplication_map(X**Integer(3))
>>> N.morphism_corestriction(h)
Traceback (most recent call last):
...
ValueError: the image of the morphism is not contained in this submodule
morphism_restriction(f)[source]

Return the restriction of \(f\) to this submodule.

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M.<v,w> = S.quotient_module((X + z)^2)
sage: N = M.span((X + z)*v)

sage: f = M.multiplication_map(X^3)
sage: f
Ore module endomorphism of Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

sage: g = N.morphism_restriction(f)
sage: g
Ore module morphism:
  From: Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
sage: g.matrix()
[        3 4*z^2 + 2]

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module((X + z)**Integer(2), names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> N = M.span((X + z)*v)

>>> f = M.multiplication_map(X**Integer(3))
>>> f
Ore module endomorphism of Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> g = N.morphism_restriction(f)
>>> g
Ore module morphism:
  From: Ore module of rank 1 over Finite Field in z of size 5^3 twisted by z |--> z^5
  To:   Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5
>>> g.matrix()
[        3 4*z^2 + 2]
rename_basis(names, coerce=False)[source]

Return the same Ore module with the given naming for the vectors in its distinguished basis.

INPUT:

  • names – a string or a list of strings, the new names

  • coerce (default: False) – a boolean; if True, a coercion map from this Ore module to renamed version is set

EXAMPLES:

sage: K.<z> = GF(5^3)
sage: S.<X> = OrePolynomialRing(K, K.frobenius_endomorphism())
sage: M = S.quotient_module(X^2 + z^2)
sage: M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

sage: Me = M.rename_basis('e')
sage: Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> K = GF(Integer(5)**Integer(3), names=('z',)); (z,) = K._first_ngens(1)
>>> S = OrePolynomialRing(K, K.frobenius_endomorphism(), names=('X',)); (X,) = S._first_ngens(1)
>>> M = S.quotient_module(X**Integer(2) + z**Integer(2))
>>> M
Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> Me = M.rename_basis('e')
>>> Me
Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5

Now compare how elements are displayed:

sage: M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
sage: Me.random_element()  # random
(2*z + 4)*e0 + (z^2 + 4*z + 4)*e1

>>> from sage.all import *
>>> M.random_element()   # random
(3*z^2 + 4*z + 2, 3*z^2 + z)
>>> Me.random_element()  # random
(2*z + 4)*e0 + (z^2 + 4*z + 4)*e1

At this point, there is no coercion map between M and Me. Therefore, adding elements in both parents results in an error:

sage: M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

>>> from sage.all import *
>>> M.random_element() + Me.random_element()
Traceback (most recent call last):
...
TypeError: unsupported operand parent(s) for +:
'Ore module of rank 2 over Finite Field in z of size 5^3 twisted by z |--> z^5' and
'Ore module <e0, e1> over Finite Field in z of size 5^3 twisted by z |--> z^5'

In order to set this coercion, one should define Me by passing the extra argument coerce=True:

sage: Me = M.rename_basis('e', coerce=True)
sage: M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2 + z + 4)*e1

>>> from sage.all import *
>>> Me = M.rename_basis('e', coerce=True)
>>> M.random_element() + Me.random_element()  # random
2*z^2*e0 + (z^2 + z + 4)*e1

Warning

Use coerce=True with extreme caution. Indeed, setting inappropriate coercion maps may result in a circular path in the coercion graph which, in turn, could eventually break the coercion system.

Note that the bracket construction also works:

sage: M.<v,w> = M.rename_basis()
sage: M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

>>> from sage.all import *
>>> M = M.rename_basis(names=('v', 'w',)); (v, w,) = M._first_ngens(2)
>>> M
Ore module <v, w> over Finite Field in z of size 5^3 twisted by z |--> z^5

In this case, \(v\) and \(w\) are automatically defined:

sage: v + w
v + w

>>> from sage.all import *
>>> v + w
v + w
class sage.modules.ore_module.ScalarAction[source]

Bases: Action

Action by scalar multiplication on Ore modules.

sage.modules.ore_module.normalize_names(names, rank)[source]

Return a normalized form of names.

INPUT:

  • names – a string, a list of strings or None

  • rank – the number of names to normalize

EXAMPLES:

sage: from sage.modules.ore_module import normalize_names

>>> from sage.all import *
>>> from sage.modules.ore_module import normalize_names

When names is a string, indices are added:

sage: normalize_names('e', 3)
('e0', 'e1', 'e2')

>>> from sage.all import *
>>> normalize_names('e', Integer(3))
('e0', 'e1', 'e2')

When names is a list or a tuple, it remains untouched except that it is always casted to a tuple (in order to be hashable and serve as a key):

sage: normalize_names(['u', 'v', 'w'], 3)
('u', 'v', 'w')

>>> from sage.all import *
>>> normalize_names(['u', 'v', 'w'], Integer(3))
('u', 'v', 'w')

Similarly, when names is None, nothing is returned:

sage: normalize_names(None, 3)

>>> from sage.all import *
>>> normalize_names(None, Integer(3))

If the number of names is not equal to rank, an error is raised:

sage: normalize_names(['u', 'v', 'w'], 2)
Traceback (most recent call last):
...
ValueError: the number of given names does not match the rank of the Ore module

>>> from sage.all import *
>>> normalize_names(['u', 'v', 'w'], Integer(2))
Traceback (most recent call last):
...
ValueError: the number of given names does not match the rank of the Ore module