# Points on schemes¶

class sage.schemes.generic.point.SchemePoint(S, parent=None)

Base class for points on a scheme, either topological or defined by a morphism.

scheme()

Return the scheme on which self is a point.

EXAMPLES:

sage: from sage.schemes.generic.point import SchemePoint
sage: S = Spec(ZZ)
sage: P = SchemePoint(S)
sage: P.scheme()
Spectrum of Integer Ring

class sage.schemes.generic.point.SchemeRationalPoint(f)

INPUT:

• f - a morphism of schemes
morphism()

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

class sage.schemes.generic.point.SchemeTopologicalPoint(S)

Base class for topological points on schemes.

class sage.schemes.generic.point.SchemeTopologicalPoint_affine_open(u, x)

INPUT:

• u – morphism with domain an affine scheme $$U$$
• x – topological point on $$U$$
affine_open()

Return the affine open subset U.

embedding_of_affine_open()

Return the embedding from the affine open subset U into this scheme.

point_on_affine()

Return the scheme point on the affine open U.

class sage.schemes.generic.point.SchemeTopologicalPoint_prime_ideal(S, P, check=False)

INPUT:

• S – an affine scheme
• P – a prime ideal of the coordinate ring of $$S$$, or anything that can be converted into such an ideal

TESTS:

sage: from sage.schemes.generic.point import SchemeTopologicalPoint_prime_ideal
sage: S = Spec(ZZ)
sage: P = SchemeTopologicalPoint_prime_ideal(S, 3); P
Point on Spectrum of Integer Ring defined by the Principal ideal (3) of Integer Ring
sage: SchemeTopologicalPoint_prime_ideal(S, 6, check=True)
Traceback (most recent call last):
...
ValueError: The argument Principal ideal (6) of Integer Ring must be a prime ideal of Integer Ring
sage: SchemeTopologicalPoint_prime_ideal(S, ZZ.ideal(7))
Point on Spectrum of Integer Ring defined by the Principal ideal (7) of Integer Ring


We define a parabola in the projective plane as a point corresponding to a prime ideal:

sage: P2.<x, y, z> = ProjectiveSpace(2, QQ)
sage: SchemeTopologicalPoint_prime_ideal(P2, y*z-x^2)
Point on Projective Space of dimension 2 over Rational Field defined by the Ideal (-x^2 + y*z) of Multivariate Polynomial Ring in x, y, z over Rational Field

prime_ideal()

Return the prime ideal that defines this scheme point.

EXAMPLES:

sage: from sage.schemes.generic.point import SchemeTopologicalPoint_prime_ideal
sage: P2.<x, y, z> = ProjectiveSpace(2, QQ)
sage: pt = SchemeTopologicalPoint_prime_ideal(P2, y*z-x^2)
sage: pt.prime_ideal()
Ideal (-x^2 + y*z) of Multivariate Polynomial Ring in x, y, z over Rational Field

sage.schemes.generic.point.is_SchemeRationalPoint(x)

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

sage.schemes.generic.point.is_SchemeTopologicalPoint(x)

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

#### Previous topic

Scheme obtained by gluing two other schemes

Ambient Spaces