Places of function fields: rational

class sage.rings.function_field.place_rational.FunctionFieldPlace_rational(parent, prime)

Bases: FunctionFieldPlace

Places of rational function fields.

degree()

Return the degree of the place.

EXAMPLES:

sage: F.<x> = FunctionField(GF(2))
sage: O = F.maximal_order()
sage: i = O.ideal(x^2 + x + 1)
sage: p = i.place()
sage: p.degree()
2

is_infinite_place()

Return True if the place is at infinite.

EXAMPLES:

sage: F.<x> = FunctionField(GF(2))
sage: F.places()
[Place (1/x), Place (x), Place (x + 1)]
sage: [p.is_infinite_place() for p in F.places()]
[True, False, False]

local_uniformizer()

Return a local uniformizer of the place.

EXAMPLES:

sage: F.<x> = FunctionField(GF(2))
sage: F.places()
[Place (1/x), Place (x), Place (x + 1)]
sage: [p.local_uniformizer() for p in F.places()]
[1/x, x, x + 1]

residue_field(name=None)

Return the residue field of the place.

EXAMPLES:

sage: F.<x> = FunctionField(GF(2))
sage: O = F.maximal_order()
sage: p = O.ideal(x^2 + x + 1).place()
sage: k, fr_k, to_k = p.residue_field()                                     # needs sage.rings.function_field
sage: k                                                                     # needs sage.rings.function_field
Finite Field in z2 of size 2^2
sage: fr_k                                                                  # needs sage.rings.function_field
Ring morphism:
  From: Finite Field in z2 of size 2^2
  To:   Valuation ring at Place (x^2 + x + 1)
sage: to_k                                                                  # needs sage.rings.function_field
Ring morphism:
  From: Valuation ring at Place (x^2 + x + 1)
  To:   Finite Field in z2 of size 2^2

valuation_ring()

Return the valuation ring at the place.

EXAMPLES:

sage: K.<x> = FunctionField(GF(2)); _.<Y> = K[]
sage: L.<y> = K.extension(Y^2 + Y + x + 1/x)                                # needs sage.rings.function_field
sage: p = L.places_finite()[0]                                              # needs sage.rings.function_field
sage: p.valuation_ring()                                                    # needs sage.rings.function_field
Valuation ring at Place (x, x*y)