Free abelian monoids

AUTHORS:

  • David Kohel (2005-09)

Sage supports free abelian monoids on any prescribed finite number \(n\geq 0\) of generators. Use the FreeAbelianMonoid function to create a free abelian monoid, and the gen and gens functions to obtain the corresponding generators. You can print the generators as arbitrary strings using the optional names argument to the FreeAbelianMonoid function.

EXAMPLE 1: It is possible to create an abelian monoid in zero or more variables; the syntax T(1) creates the monoid identity element even in the rank zero case.

sage: T = FreeAbelianMonoid(0, '')
sage: T
Free abelian monoid on 0 generators ()
sage: T.gens()
()
sage: T(1)
1

EXAMPLE 2: A free abelian monoid uses a multiplicative representation of elements, but the underlying representation is lists of integer exponents.

sage: F = FreeAbelianMonoid(5,names='a,b,c,d,e')
sage: (a,b,c,d,e) = F.gens()
sage: a*b^2*e*d
a*b^2*d*e
sage: x = b^2*e*d*a^7
sage: x
a^7*b^2*d*e
sage: x.list()
[7, 2, 0, 1, 1]
class sage.monoids.free_abelian_monoid.FreeAbelianMonoidFactory

Bases: sage.structure.factory.UniqueFactory

Create the free abelian monoid in \(n\) generators.

INPUT:

  • n - integer
  • names - names of generators

OUTPUT: free abelian monoid

EXAMPLES:

sage: FreeAbelianMonoid(0, '')
Free abelian monoid on 0 generators ()
sage: F = FreeAbelianMonoid(5,names = list("abcde"))
sage: F
Free abelian monoid on 5 generators (a, b, c, d, e)
sage: F(1)
1
sage: (a, b, c, d, e) = F.gens()
sage: mul([ a, b, a, c, b, d, c, d ], F(1))
a^2*b^2*c^2*d^2
sage: a**2 * b**3 * a**2 * b**4
a^4*b^7
sage: loads(dumps(F)) is F
True
create_key(n, names)

x.__init__(...) initializes x; see help(type(x)) for signature

create_object(version, key)

x.__init__(...) initializes x; see help(type(x)) for signature

class sage.monoids.free_abelian_monoid.FreeAbelianMonoid_class(n, names)

Bases: sage.structure.parent_gens.ParentWithGens

Free abelian monoid on \(n\) generators.

gen(i=0)

The \(i\)-th generator of the abelian monoid.

EXAMPLES:

sage: F = FreeAbelianMonoid(5,'a')
sage: F.gen(0)
a0
sage: F.gen(2)
a2
ngens()

The number of free generators of the abelian monoid.

EXAMPLES:

sage: F = FreeAbelianMonoid(3000, 'a')
sage: F.ngens()
3000
sage.monoids.free_abelian_monoid.is_FreeAbelianMonoid(x)

Return True if \(x\) is a free abelian monoid.

EXAMPLES:

sage: from sage.monoids.free_abelian_monoid import is_FreeAbelianMonoid
sage: is_FreeAbelianMonoid(5)
False
sage: is_FreeAbelianMonoid(FreeAbelianMonoid(7,'a'))
True
sage: is_FreeAbelianMonoid(FreeMonoid(7,'a'))
False
sage: is_FreeAbelianMonoid(FreeMonoid(0,''))
False

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