Plane conic constructor#

AUTHORS:

  • Marco Streng (2010-07-20)

  • Nick Alexander (2008-01-08)

sage.schemes.plane_conics.constructor.Conic(base_field, F=None, names=None, unique=True)[source]#

Return the plane projective conic curve defined by F over base_field.

The input form Conic(F, names=None) is also accepted, in which case the fraction field of the base ring of F is used as base field.

INPUT:

  • base_field – The base field of the conic.

  • names – a list, tuple, or comma separated string of three variable names specifying the names of the coordinate functions of the ambient space \(\Bold{P}^3\). If not specified or read off from F, then this defaults to 'x,y,z'.

  • F – a polynomial, list, matrix, ternary quadratic form, or list or tuple of 5 points in the plane.

    If F is a polynomial or quadratic form, then the output is the curve in the projective plane defined by F = 0.

    If F is a polynomial, then it must be a polynomial of degree at most 2 in 2 variables, or a homogeneous polynomial in of degree 2 in 3 variables.

    If F is a matrix, then the output is the zero locus of \((x,y,z) F (x,y,z)^t\).

    If F is a list of coefficients, then it has length 3 or 6 and gives the coefficients of the monomials \(x^2, y^2, z^2\) or all 6 monomials \(x^2, xy, xz, y^2, yz, z^2\) in lexicographic order.

    If F is a list of 5 points in the plane, then the output is a conic through those points.

  • unique – Used only if F is a list of points in the plane. If the conic through the points is not unique, then raise ValueError if and only if unique is True

OUTPUT:

A plane projective conic curve defined by F over a field.

EXAMPLES:

Conic curves given by polynomials

sage: X,Y,Z = QQ['X,Y,Z'].gens()
sage: Conic(X^2 - X*Y + Y^2 - Z^2)
Projective Conic Curve over Rational Field defined by X^2 - X*Y + Y^2 - Z^2
sage: x,y = GF(7)['x,y'].gens()
sage: Conic(x^2 - x + 2*y^2 - 3, 'U,V,W')
Projective Conic Curve over Finite Field of size 7
 defined by U^2 + 2*V^2 - U*W - 3*W^2

>>> from sage.all import *
>>> X,Y,Z = QQ['X,Y,Z'].gens()
>>> Conic(X**Integer(2) - X*Y + Y**Integer(2) - Z**Integer(2))
Projective Conic Curve over Rational Field defined by X^2 - X*Y + Y^2 - Z^2
>>> x,y = GF(Integer(7))['x,y'].gens()
>>> Conic(x**Integer(2) - x + Integer(2)*y**Integer(2) - Integer(3), 'U,V,W')
Projective Conic Curve over Finite Field of size 7
 defined by U^2 + 2*V^2 - U*W - 3*W^2

Conic curves given by matrices

sage: Conic(matrix(QQ, [[1, 2, 0], [4, 0, 0], [7, 0, 9]]), 'x,y,z')
Projective Conic Curve over Rational Field defined by x^2 + 6*x*y + 7*x*z + 9*z^2

sage: x,y,z = GF(11)['x,y,z'].gens()
sage: C = Conic(x^2 + y^2 - 2*z^2); C
Projective Conic Curve over Finite Field of size 11 defined by x^2 + y^2 - 2*z^2
sage: Conic(C.symmetric_matrix(), 'x,y,z')
Projective Conic Curve over Finite Field of size 11 defined by x^2 + y^2 - 2*z^2

>>> from sage.all import *
>>> Conic(matrix(QQ, [[Integer(1), Integer(2), Integer(0)], [Integer(4), Integer(0), Integer(0)], [Integer(7), Integer(0), Integer(9)]]), 'x,y,z')
Projective Conic Curve over Rational Field defined by x^2 + 6*x*y + 7*x*z + 9*z^2

>>> x,y,z = GF(Integer(11))['x,y,z'].gens()
>>> C = Conic(x**Integer(2) + y**Integer(2) - Integer(2)*z**Integer(2)); C
Projective Conic Curve over Finite Field of size 11 defined by x^2 + y^2 - 2*z^2
>>> Conic(C.symmetric_matrix(), 'x,y,z')
Projective Conic Curve over Finite Field of size 11 defined by x^2 + y^2 - 2*z^2

Conics given by coefficients

sage: Conic(QQ, [1,2,3])
Projective Conic Curve over Rational Field defined by x^2 + 2*y^2 + 3*z^2
sage: Conic(GF(7), [1,2,3,4,5,6], 'X')
Projective Conic Curve over Finite Field of size 7
defined by X0^2 + 2*X0*X1 - 3*X1^2 + 3*X0*X2 - 2*X1*X2 - X2^2

>>> from sage.all import *
>>> Conic(QQ, [Integer(1),Integer(2),Integer(3)])
Projective Conic Curve over Rational Field defined by x^2 + 2*y^2 + 3*z^2
>>> Conic(GF(Integer(7)), [Integer(1),Integer(2),Integer(3),Integer(4),Integer(5),Integer(6)], 'X')
Projective Conic Curve over Finite Field of size 7
defined by X0^2 + 2*X0*X1 - 3*X1^2 + 3*X0*X2 - 2*X1*X2 - X2^2

The conic through a set of points

sage: C = Conic(QQ, [[10,2],[3,4],[-7,6],[7,8],[9,10]]); C
Projective Conic Curve over Rational Field
 defined by x^2 + 13/4*x*y - 17/4*y^2 - 35/2*x*z + 91/4*y*z - 37/2*z^2
sage: C.rational_point()
(10 : 2 : 1)
sage: C.point([3,4])
(3 : 4 : 1)

sage: a = AffineSpace(GF(13), 2)
sage: Conic([a([x,x^2]) for x in range(5)])
Projective Conic Curve over Finite Field of size 13 defined by x^2 - y*z

>>> from sage.all import *
>>> C = Conic(QQ, [[Integer(10),Integer(2)],[Integer(3),Integer(4)],[-Integer(7),Integer(6)],[Integer(7),Integer(8)],[Integer(9),Integer(10)]]); C
Projective Conic Curve over Rational Field
 defined by x^2 + 13/4*x*y - 17/4*y^2 - 35/2*x*z + 91/4*y*z - 37/2*z^2
>>> C.rational_point()
(10 : 2 : 1)
>>> C.point([Integer(3),Integer(4)])
(3 : 4 : 1)

>>> a = AffineSpace(GF(Integer(13)), Integer(2))
>>> Conic([a([x,x**Integer(2)]) for x in range(Integer(5))])
Projective Conic Curve over Finite Field of size 13 defined by x^2 - y*z