Ideals in multivariate polynomial rings.¶

Sage has a powerful system to compute with multivariate polynomial rings. Most algorithms dealing with these ideals are centered the computation of Groebner bases. Sage mainly uses Singular to implement this functionality. Singular is widely regarded as the best open-source system for Groebner basis calculation in multivariate polynomial rings over fields.

AUTHORS:

William Stein
Kiran S. Kedlaya (2006-02-12): added Macaulay2 analogues of some Singular features
Martin Albrecht (2008,2007): refactoring, many Singular related functions
Martin Albrecht (2009): added Groebner basis over rings functionality from Singular 3.1

EXAMPLES:

We compute a Groebner basis for some given ideal. The type returned by the groebner_basis method is Sequence, i.e. it is not a MPolynomialIdeal:

sage: x,y,z = QQ['x,y,z'].gens()
sage: I = ideal(x^5 + y^4 + z^3 - 1,  x^3 + y^3 + z^2 - 1)
sage: B = I.groebner_basis()
sage: type(B)
<class 'sage.structure.sequence.Sequence'>

Groebner bases can be used to solve the ideal membership problem:

sage: f,g,h = B
sage: (2*x*f + g).reduce(B)
0

sage: (2*x*f + g) in I
True

sage: (2*x*f + 2*z*h + y^3).reduce(B)
y^3

sage: (2*x*f + 2*z*h + y^3) in I
False

We compute a Groebner basis for Cyclic 6, which is a standard benchmark and test ideal.

sage: R.<x,y,z,t,u,v> = QQ['x,y,z,t,u,v']
sage: I = sage.rings.ideal.Cyclic(R,6)
sage: B = I.groebner_basis()
sage: len(B)
45

We compute in a quotient of a polynomial ring over $\ZZ/17\ZZ$ :

sage: R.<x,y> = ZZ[]
sage: S.<a,b> = R.quotient((x^2 + y^2, 17))
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Integer Ring
by the ideal (x^2 + y^2, 17)

sage: a^2 + b^2 == 0
True
sage: a^3 - b^2
-a*b^2 - b^2

Note that the result of a computation is not necessarily reduced:

sage: (a+b)^17
256*a*b^16 + 256*b^17
sage: S(17) == 0
True

Or we can work with $\ZZ/17\ZZ`$ directly:

sage: R.<x,y> = Zmod(17)[]
sage: S.<a,b> = R.quotient((x^2 + y^2,))
sage: S
Quotient of Multivariate Polynomial Ring in x, y over Ring of
integers modulo 17 by the ideal (x^2 + y^2)

sage: a^2 + b^2 == 0
True
sage: a^3 - b^2
-a*b^2 - b^2
sage: (a+b)^17
a*b^16 + b^17
sage: S(17) == 0
True

Working with a polynomial ring over $\ZZ$ :

sage: R.<x,y,z,w> = ZZ[]
sage: I = ideal(x^2 + y^2 - z^2 - w^2, x-y)
sage: J = I^2
sage: J.groebner_basis()
[4*y^4 - 4*y^2*z^2 + z^4 - 4*y^2*w^2 + 2*z^2*w^2 + w^4, 
 2*x*y^2 - 2*y^3 - x*z^2 + y*z^2 - x*w^2 + y*w^2, 
 x^2 - 2*x*y + y^2]

sage: y^2 - 2*x*y + x^2 in J
True
sage: 0 in J
True

We do a Groebner basis computation over a number field:

sage: K.<zeta> = CyclotomicField(3)
sage: R.<x,y,z> = K[]; R
Multivariate Polynomial Ring in x, y, z over Cyclotomic Field of order 3 and degree 2

sage: i = ideal(x - zeta*y + 1, x^3 - zeta*y^3); i
Ideal (x + (-zeta)*y + 1, x^3 + (-zeta)*y^3) of Multivariate
Polynomial Ring in x, y, z over Cyclotomic Field of order 3 and degree 2

sage: i.groebner_basis()
[y^3 + (2*zeta + 1)*y^2 + (zeta - 1)*y + (-1/3*zeta - 2/3), x + (-zeta)*y + 1]

sage: S = R.quotient(i); S
Quotient of Multivariate Polynomial Ring in x, y, z over
Cyclotomic Field of order 3 and degree 2 by the ideal (x +
(-zeta)*y + 1, x^3 + (-zeta)*y^3)

sage: S.0  - zeta*S.1
-1
sage: S.0^3 - zeta*S.1^3
0

Two examples from the Mathematica documentation (done in Sage):

We compute a Groebner basis:

sage: R.<x,y> = PolynomialRing(QQ, order='lex')
sage: ideal(x^2 - 2*y^2, x*y - 3).groebner_basis()
 [x - 2/3*y^3, y^4 - 9/2]

We show that three polynomials have no common root:

sage: R.<x,y> = QQ[]
sage: ideal(x+y, x^2 - 1, y^2 - 2*x).groebner_basis()
[1]

The next example shows how we can use Groebner bases over $\ZZ$ to find the primes modulo which a system of equations has a solution, when the system has no solutions over the rationals.

We first form a certain ideal $I$ in $\ZZ[x, y, z]$ , and note that the Groebner basis of $I$ over $\QQ$ contains 1, so there are no solutions over $\QQ$ or an algebraic closure of it (this is not surprising as there are 4 equations in 3 unknowns).
sage: P.<x,y,z> = PolynomialRing(ZZ,order='lex')
sage: I = ideal(-y^2 - 3*y + z^2 + 3, -2*y*z + z^2 + 2*z + 1, \
                x*z + y*z + z^2, -3*x*y + 2*y*z + 6*z^2)
sage: I.change_ring(P.change_ring(QQ)).groebner_basis()
[1]
However, when we compute the Groebner basis of I (defined over $\ZZ`$ ), we note that there is a certain integer in the ideal which is not 1.
sage: I.groebner_basis()
[-x - y - z, -y^2 - 3*y + z^2 + 3, -y*z + 14329*y + 6653454247350, 
 2*y - 1199*z^3 + 74229*z^2 + 31017*z + 106019, -23*z^3 + 953554642851*z + 2034, 
 19*z^2 + 5357048579, 2*z - 1339262138, 164878]
Now for each prime $p$ dividing this integer 164878, the Groebner basis of I modulo $p$ will be non-trivial and will thus give a solution of the original system modulo $p$ .
sage: factor(164878)
2 * 7 * 11777

sage: I.change_ring(P.change_ring( GF(2) )).groebner_basis()
[x + y + z, y^2 + y, y*z + y, z^2 + 1]
sage: I.change_ring(P.change_ring( GF(7) )).groebner_basis()
[x - 1, y + 3, z - 2]
sage: I.change_ring(P.change_ring( GF(11777 ))).groebner_basis()
[x + 5633, y - 3007, z - 2626]
The Groebner basis modulo any product of the prime factors is also non-trivial.
sage: I.change_ring(P.change_ring( IntegerModRing(2*7) )).groebner_basis()
[x*y + 10, x*z + 13*y + 9, 7*x + 7*y + 7*z, y^2 + 3*y, y*z + y + 2, 2*y + 6, z^2 + 3, 2*z + 10]
Modulo any other prime the Groebner basis is trivial so there are no other solutions. For example:
sage: I.change_ring( P.change_ring( GF(3) ) ).groebner_basis()
[1]

TESTS:

sage: x,y,z = QQ['x,y,z'].gens()
sage: I = ideal(x^5 + y^4 + z^3 - 1,  x^3 + y^3 + z^2 - 1)
sage: I == loads(dumps(I))
True

class sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal(ring, gens, coerce=True)¶

Bases: sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_singular_repr, sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_macaulay2_repr, sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_magma_repr, sage.rings.ideal.Ideal_generic

change_ring(P)¶

Return the ideal I in P spanned by the generators $g_1, ..., g_n$ of self as returned by self.gens().

INPUT:

P - a multivariate polynomial ring

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(QQ,3,order='lex')
sage: I = sage.rings.ideal.Cyclic(P)
sage: I
Ideal (x + y + z, x*y + x*z + y*z, x*y*z - 1) of
Multivariate Polynomial Ring in x, y, z over Rational Field

sage: I.groebner_basis()
[x + y + z, y^2 + y*z + z^2, z^3 - 1]

sage: Q.<x,y,z> = P.change_ring(order='degrevlex'); Q
Multivariate Polynomial Ring in x, y, z over Rational Field
sage: Q.term_order()
Degree reverse lexicographic term order

sage: J = I.change_ring(Q); J
Ideal (x + y + z, x*y + x*z + y*z, x*y*z - 1) of
Multivariate Polynomial Ring in x, y, z over Rational Field

sage: J.groebner_basis()
[z^3 - 1, y^2 + y*z + z^2, x + y + z]

groebner_basis(*args, **kwds)¶

Return the reduced Groebner basis of this ideal. A Groebner basis $g_1,...,g_n$ for an ideal $I$ is a basis such that $<LM(g_i)> = LM(I)$ , i.e., the leading monomial ideal of $I$ is spanned by the leading terms of $g_1,...,g_n$ . Groebner bases are the key concept in computational ideal theory in multivariate polynomial rings which allows a variety of problems to be solved. Additionally, a reduced Groebner basis $G$ is a unique representation for the ideal $<G>$ with respect to the chosen monomial ordering.

INPUT:

algorithm - determines the algorithm to use, see below for available algorithms.
*args - additional parameters passed to the respective implementations
**kwds - additional keyword parameters passed to the respective implementations

ALGORITHMS:

‘’: autoselect (default)
‘singular:groebner’: Singular’s groebner command
‘singular:std’: Singular’s std command
‘singular:stdhilb’: Singular’s stdhib command
‘singular:stdfglm’: Singular’s stdfglm command
‘singular:slimgb’: Singular’s slimgb command
‘libsingular:groebner’: libSingular’s groebner command
‘libsingular:std’: libSingular’s std command
‘libsingular:slimgb’: libSingular’s slimgb command
‘libsingular:stdhilb’: libSingular’s stdhib command
‘libsingular:stdfglm’: libSingular’s stdfglm command
‘toy:buchberger’: Sage’s toy/educational buchberger without Buchberger criteria
‘toy:buchberger2’: Sage’s toy/educational buchberger with Buchberger criteria
‘toy:d_basis’: Sage’s toy/educational algorithm for computation over PIDs
‘macaulay2:gb’: Macaulay2’s gb command (if available)
‘magma:GroebnerBasis’: Magma’s Groebnerbasis command (if available)

If only a system is given - e.g. ‘magma’ - the default algorithm is chosen for that system.

Note

The Singular and libSingular versions of the respective algorithms are identical, but the former calls an external Singular process while the later calls a C function, i.e. the calling overhead is smaller.

EXAMPLES:

Consider Katsura-3 over QQ with lexicographical term ordering. We compute the reduced Groebner basis using every available implementation and check their equality.

sage: P.<a,b,c> = PolynomialRing(QQ,3, order='lex')
sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis()
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('libsingular:groebner')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('libsingular:std')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('libsingular:stdhilb')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('libsingular:stdfglm')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('libsingular:slimgb')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

Note that toy:buchberger does not return the reduced Groebner basis,

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('toy:buchberger')
[a^2 - a + 2*b^2 + 2*c^2, 
 a*b + b*c - 1/2*b, a + 2*b + 2*c - 1, 
 b^2 + 3*b*c - 1/2*b + 3*c^2 - c,
 b*c - 1/10*b + 6/5*c^2 - 2/5*c, 
 b + 30*c^3 - 79/7*c^2 + 3/7*c, 
 c^6 - 79/210*c^5 - 229/2100*c^4 + 121/2520*c^3 + 1/3150*c^2 - 11/12600*c, 
 c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

but that toy:buchberger2 does.

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('toy:buchberger2')
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('macaulay2:gb') # optional - macaulay2
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

sage: I = sage.rings.ideal.Katsura(P,3) # regenerate to prevent caching
sage: I.groebner_basis('magma:GroebnerBasis') # optional - magma
[a - 60*c^3 + 158/7*c^2 + 8/7*c - 1, b + 30*c^3 - 79/7*c^2 + 3/7*c, c^4 - 10/21*c^3 + 1/84*c^2 + 1/84*c]

Groebner bases over $\ZZ$ can be computed.

sage: P.<a,b,c> = PolynomialRing(ZZ,3)
sage: I = P * (a + 2*b + 2*c - 1, a^2 - a + 2*b^2 + 2*c^2, 2*a*b + 2*b*c - b)
sage: I.groebner_basis()
[-b^3 + 23*b*c^2 - 3*b^2 - 5*b*c, 
 2*b*c^2 - 6*c^3 - b^2 - b*c + 2*c^2, 
 42*c^3 + 5*b^2 + 4*b*c - 14*c^2, 
 2*b^2 + 6*b*c + 6*c^2 - b - 2*c, 
 -10*b*c - 12*c^2 + b + 4*c, 
 a + 2*b + 2*c - 1]

sage: I.groebner_basis('macaulay2') # optional - macaulay2 
[b^3 + b*c^2 + 12*c^3 + b^2 + b*c - 4*c^2, 
 2*b*c^2 - 6*c^3 + b^2 + 5*b*c + 8*c^2 - b - 2*c, 
 42*c^3 + b^2 + 2*b*c - 14*c^2 + b, 
 2*b^2 - 4*b*c - 6*c^2 + 2*c, 10*b*c + 12*c^2 - b - 4*c, 
 a + 2*b + 2*c - 1]

Groebner bases over $\ZZ/n\ZZ$ are also supported:

sage: P.<a,b,c> = PolynomialRing(Zmod(1000),3)
sage: I = P * (a + 2*b + 2*c - 1, a^2 - a + 2*b^2 + 2*c^2, 2*a*b + 2*b*c - b)
sage: I.groebner_basis()
[b*c^2 + 992*b*c + 712*c^2 + 332*b + 96*c, 
 2*c^3 + 589*b*c + 862*c^2 + 762*b + 268*c, 
 b^2 + 438*b*c + 281*b, 
 5*b*c + 156*c^2 + 112*b + 948*c, 
 50*c^2 + 600*b + 650*c, a + 2*b + 2*c + 999, 125*b]

Sage also supports local orderings:

sage: P.<x,y,z> = PolynomialRing(QQ,3,order='negdegrevlex')
sage: I = P * (  x*y*z + z^5, 2*x^2 + y^3 + z^7, 3*z^5 +y ^5 )
sage: I.groebner_basis()
[x^2 + 1/2*y^3, x*y*z + z^5, y^5 + 3*z^5, y^4*z - 2*x*z^5, z^6]

We can represent every element in the ideal as a combination of the generators using the lift() method:

sage: P.<x,y,z> = PolynomialRing(QQ,3)
sage: I = P * ( x*y*z + z^5, 2*x^2 + y^3 + z^7, 3*z^5 +y ^5 )
sage: J = Ideal(I.groebner_basis())
sage: f = sum(P.random_element(terms=2)*f for f in I.gens())
sage: f
1/2*y^2*z^7 - 1/4*y*z^8 + 2*x*z^5 + 95*z^6 + 1/2*y^5 - 1/4*y^4*z + x^2*y^2 + 3/2*x^2*y*z + 95*x*y*z^2
sage: f.lift(I.gens())
[2*x + 95*z, 1/2*y^2 - 1/4*y*z, 0]
sage: l = f.lift(J.gens()); l
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1/2*y^2 + 1/4*y*z, 1/2*y^2*z^2 - 1/4*y*z^3 + 2*x + 95*z]
sage: sum(map(mul, zip(l,J.gens()))) == f
True

Groebner bases over fraction fields of polynomial rings are also supported:

sage: P.<t> = QQ[]
sage: F = Frac(P)
sage: R.<X,Y,Z> = F[]
sage: I = Ideal([f + P.random_element() for f in sage.rings.ideal.Katsura(R).gens()])
sage: I.groebner_basis()
[Z^3 + (79/105*t^2 - 79/105*t + 79/630)*Z^2 + (-11/105*t^4 + 22/105*t^3 - 17/45*t^2 + 197/630*t + 557/1890)*Y + ...,
Y^2 + (-3/5)*Z^2 + (2/5*t^2 - 2/5*t + 1/15)*Y + (-2/5*t^2 + 2/5*t - 1/15)*Z - 1/10*t^4 + 1/5*t^3 - 7/30*t^2 + 2/5*t + 11/90, 
Y*Z + 6/5*Z^2 + (1/5*t^2 - 1/5*t + 1/30)*Y + (4/5*t^2 - 4/5*t + 2/15)*Z + 1/5*t^4 - 2/5*t^3 + 7/15*t^2 - 3/10*t - 11/45, X + 2*Y + 2*Z + t^2 - t - 1/3]

ALGORITHM: Uses Singular, Magma (if available), Macaulay2 (if available), or a toy implementation.

groebner_fan(is_groebner_basis=False, symmetry=None, verbose=False)¶

Return the Groebner fan of this ideal.

The base ring must be $\QQ$ or a finite field $\GF{p}$ of with $p <= 32749$ .

EXAMPLES:

sage: P.<x,y> = PolynomialRing(QQ)
sage: i = ideal(x^2 - y^2 + 1)
sage: g = i.groebner_fan()
sage: g.reduced_groebner_bases()
[[x^2 - y^2 + 1], [-x^2 + y^2 - 1]]

INPUT:

is_groebner_basis - bool (default False). if True, then I.gens() must be a Groebner basis with respect to the standard degree lexicographic term order.
symmetry - default: None; if not None, describes symmetries of the ideal
verbose - default: False; if True, printout useful info during computations

homogenize(var='h')¶

Return homogeneous ideal spanned by the homogeneous polynomials generated by homogenizing the generators of this ideal.

INPUT:

h - variable name or variable in cover ring (default: ‘h’)

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(GF(2))
sage: I = Ideal([x^2*y + z + 1, x + y^2 + 1]); I
Ideal (x^2*y + z + 1, y^2 + x + 1) of Multivariate
Polynomial Ring in x, y, z over Finite Field of size 2

sage: I.homogenize()
Ideal (x^2*y + z*h^2 + h^3, y^2 + x*h + h^2) of
Multivariate Polynomial Ring in x, y, z, h over Finite
Field of size 2

sage: I.homogenize(y)
Ideal (x^2*y + y^3 + y^2*z, x*y) of Multivariate
Polynomial Ring in x, y, z over Finite Field of size 2

       sage: I = Ideal([x^2*y + z^3 + y^2*x, x + y^2 + 1])
sage: I.homogenize()
Ideal (x^2*y + x*y^2 + z^3, y^2 + x*h + h^2) of
Multivariate Polynomial Ring in x, y, z, h over Finite
Field of size 2

is_homogeneous()¶

Return True if this ideal is spanned by homogeneous polynomials, i.e. if it is a homogeneous ideal.

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(QQ,3)
sage: I = sage.rings.ideal.Katsura(P)
sage: I
Ideal (x + 2*y + 2*z - 1, x^2 + 2*y^2 + 2*z^2 - x, 2*x*y +
2*y*z - y) of Multivariate Polynomial Ring in x, y, z over
Rational Field

sage: I.is_homogeneous()
False

sage: J = I.homogenize()
sage: J
Ideal (x + 2*y + 2*z - h, x^2 + 2*y^2 + 2*z^2 - x*h, 2*x*y
+ 2*y*z - y*h) of Multivariate Polynomial Ring in x, y, z,
h over Rational Field

sage: J.is_homogeneous()
True

normal_basis(*args, **kwds)¶

Returns a vector space basis (consisting of monomials) of the quotient ring by the ideal, resp. of a free module by the module, in case it is finite dimensional and if the input is a standard basis with respect to the ring ordering.

INPUT: algorithm - defaults to use libsingular, if it is anything else we will use the kbase() command

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ)
sage: I = R.ideal(x^2+y^2+z^2-4, x^2+2*y^2-5, x*z-1)
sage: I.normal_basis()
[y*z^2, z^2, y*z, z, x*y, y, x, 1]
sage: I.normal_basis(algorithm='singular')
[y*z^2, z^2, y*z, z, x*y, y, x, 1]

plot(*args, **kwds)¶

Plot the real zero locus of this principal ideal.

INPUT:

self - a principal ideal in 2 variables
algorithm - set this to ‘surf’ if you want ‘surf’ to

plot the ideal (default: None)
*args - optional tuples (variable, minimum, maximum)

for plotting dimensions
**kwds - optional keyword arguments passed on to

implicit_plot

EXAMPLES:

Implicit plotting in 2-d:

sage: R.<x,y> = PolynomialRing(QQ,2)
sage: I = R.ideal([y^3 - x^2])
sage: I.plot()                         # cusp 

sage: I = R.ideal([y^2 - x^2 - 1])
sage: I.plot((x,-3, 3), (y, -2, 2))  # hyperbola

sage: I = R.ideal([y^2 + x^2*(1/4) - 1])
sage: I.plot()                         # ellipse

sage: I = R.ideal([y^2-(x^2-1)*(x-2)])
sage: I.plot()                         # elliptic curve

sage: f = ((x+3)^3 + 2*(x+3)^2 - y^2)*(x^3 - y^2)*((x-3)^3-2*(x-3)^2-y^2)
sage: I = R.ideal(f)
sage: I.plot()                         # the Singular logo

This used to be trac #5267:

sage: I = R.ideal([-x^2*y+1])
sage: I.plot()

AUTHORS:

Martin Albrecht (2008-09)

reduce(f)¶

Reduce an element modulo the reduced Groebner basis for this ideal. This returns 0 if and only if the element is in this ideal. In any case, this reduction is unique up to monomial orders.

EXAMPLES:

sage: R.<x,y> = PolynomialRing(QQ, 2)
sage: I = (x^3 + y, y)*R
sage: I.reduce(y)
0
sage: I.reduce(x^3)
0
sage: I.reduce(x - y)
x

sage: I = (y^2 - (x^3 + x))*R
sage: I.reduce(x^3)
y^2 - x
sage: I.reduce(x^6)
y^4 - 2*x*y^2 + x^2
sage: (y^2 - x)^2
y^4 - 2*x*y^2 + x^2

Note

Requires computation of a Groebner basis, which can be a very expensive operation.

weil_restriction(*args, **kwds)¶

Compute the Weil restriction of this ideal over some extension field.

A Weil restriction of scalars - denoted $Res_{L/k}$ - is a functor which, for any finite extension of fields $L/k$ and any algebraic variety $X$ over $L$ , produces another corresponding variety $Res_{L/k}(X)$ , defined over $k$ . It is useful for reducing questions about varieties over large fields to questions about more complicated varieties over smaller fields.

This function does not compute this Weil restriction directly but computes on generating sets of polynomial ideals:

Let $d$ be the degree of the field extension $L/k$ , let $a$ a generator of $L/k$ and $p$ the minimal polynomial of $L/k$ . Denote this ideal by $I$ .

Specifically, this function first maps each variable $x$ to its representation over $k$ : $\sum_{i=0}^{d-1} a^i x_i$ . Then each generator of $I$ is evaluated over these representations and reduced modulo the minimal polynomial $p$ . The result is interpreted as a univariate polynomial in $a$ and its coefficients are the new generators of the returned ideal.

If the input and the output ideals are radical, this is equivalent to the statement about algebraic varieties above.

EXAMPLE:

sage: k.<a> = GF(2^2)
sage: P.<x,y> = PolynomialRing(k,2)
sage: I = Ideal([x*y + 1, a*x + 1])
sage: I.variety()
[{y: a, x: a + 1}]
sage: J = I.weil_restriction()
sage: J
Ideal (x1*y0 + x0*y1 + x1*y1, x0*y0 + x1*y1 + 1, x0 + x1, x1 + 1) of
Multivariate Polynomial Ring in x0, x1, y0, y1 over Finite Field of size 2
sage: J += sage.rings.ideal.FieldIdeal(J.ring()) # ensure radical ideal
sage: J.variety()
[{y1: 1, x1: 1, x0: 1, y0: 0}]

sage: J.weil_restriction() # returns J
Ideal (x1*y0 + x0*y1 + x1*y1, x0*y0 + x1*y1 + 1, x0 + x1, x1 + 1, x0^2 + x0, 
       x1^2 + x1, y0^2 + y0, y1^2 + y1) 
       of Multivariate Polynomial Ring in x0, x1, y0, y1 over Finite Field of size 2

sage: k.<a> = GF(3^5)
sage: P.<x,y,z> = PolynomialRing(k)
sage: I = sage.rings.ideal.Katsura(P)
sage: I.dimension()
0
sage: I.variety()
[{y: 0, z: 0, x: 1}]

sage: J = I.weil_restriction(); J
Ideal (x4 - y4 - z4, x3 - y3 - z3, x2 - y2 - z2, x1 - y1 - z1, x0 - y0 - z0 - 1, 
       x2^2 - x1*x3 - x0*x4 + x4^2 - y2^2 + y1*y3 + y0*y4 - y4^2 - z2^2 + z1*z3 + z0*z4 - z4^2 - x4, 
       -x1*x2 - x0*x3 - x3*x4 - x4^2 + y1*y2 + y0*y3 + y3*y4 + y4^2 + z1*z2 + z0*z3 + z3*z4 + z4^2 - x3, 
       x1^2 - x0*x2 + x3^2 - x2*x4 + x3*x4 - y1^2 + y0*y2 - y3^2 + y2*y4 - y3*y4 - z1^2 + z0*z2 - z3^2 + z2*z4 - z3*z4 - x2, 
       -x0*x1 - x2*x3 - x3^2 - x1*x4 + x2*x4 + y0*y1 + y2*y3 + y3^2 + y1*y4 - y2*y4 + z0*z1 + z2*z3 + z3^2 + z1*z4 - z2*z4 - x1, 
       x0^2 + x2*x3 + x1*x4 - y0^2 - y2*y3 - y1*y4 - z0^2 - z2*z3 - z1*z4 - x0, 
       -x4*y0 - x3*y1 - x2*y2 - x1*y3 - x0*y4 - x4*y4 - y4*z0 - y3*z1 - y2*z2 - y1*z3 - y0*z4 - y4*z4 - y4, 
       -x3*y0 - x2*y1 - x1*y2 - x0*y3 - x4*y3 - x3*y4 + x4*y4 - y3*z0 - y2*z1 - y1*z2 - y0*z3 - y4*z3 - y3*z4 + y4*z4 - y3, 
       -x2*y0 - x1*y1 - x0*y2 - x4*y2 - x3*y3 + x4*y3 - x2*y4 + x3*y4 - y2*z0 - y1*z1 - y0*z2 - y4*z2 - y3*z3 + y4*z3 - y2*z4 + y3*z4 - y2, 
       -x1*y0 - x0*y1 - x4*y1 - x3*y2 + x4*y2 - x2*y3 + x3*y3 - x1*y4 + x2*y4 - y1*z0 - y0*z1 - y4*z1 - y3*z2 + y4*z2 - y2*z3 + y3*z3 - y1*z4 + y2*z4 - y1, 
       -x0*y0 + x4*y1 + x3*y2 + x2*y3 + x1*y4 - y0*z0 + y4*z1 + y3*z2 + y2*z3 + y1*z4 - y0) of Multivariate Polynomial Ring in 
       x0, x1, x2, x3, x4, y0, y1, y2, y3, y4, z0, z1, z2, z3, z4 over Finite Field of size 3
sage: J += sage.rings.ideal.FieldIdeal(J.ring()) # ensure radical ideal
sage: J.variety()
[{y1: 0, y4: 0, x4: 0, y2: 0, y3: 0, y0: 0, x2: 0, z4: 0, z3: 0, z2: 0, x1: 0, z1: 0, z0: 0, x0: 1, x3: 0}]

Weil restrictions are often used to study elliptic curves over extension fields so we give a simple example involving those:

sage: K.<a> = QuadraticField(1/3)
sage: E = EllipticCurve(K,[1,2,3,4,5])

We pick a point on E:

sage: p = E.lift_x(1); p 
(1 : 2 : 1)

sage: I = E.defining_ideal(); I
Ideal (-x^3 - 2*x^2*z + x*y*z + y^2*z - 4*x*z^2 + 3*y*z^2 - 5*z^3) 
of Multivariate Polynomial Ring in x, y, z over Number Field in a with defining polynomial x^2 - 1/3

Of course, the point p is a root of all generators of I:

sage: [f.subs(x=1,y=2,z=1) for f in I.gens()]
[0]

I is also radical:

sage: I.radical() == I
True

So we compute its Weil restriction:

sage: J = I.weil_restriction()
sage: J
Ideal (-3*x0^2*x1 - 1/3*x1^3 - 4*x0*x1*z0 + x1*y0*z0 + x0*y1*z0 + 2*y0*y1*z0 - 4*x1*z0^2 + 3*y1*z0^2 - 2*x0^2*z1 
        - 2/3*x1^2*z1 + x0*y0*z1 + y0^2*z1 + 1/3*x1*y1*z1 + 1/3*y1^2*z1 - 8*x0*z0*z1 + 6*y0*z0*z1 - 15*z0^2*z1 - 4/3*x1*z1^2 + y1*z1^2 - 5/3*z1^3, 
       -x0^3 - x0*x1^2 - 2*x0^2*z0 - 2/3*x1^2*z0 + x0*y0*z0 + y0^2*z0 + 1/3*x1*y1*z0 + 1/3*y1^2*z0 - 4*x0*z0^2 + 3*y0*z0^2 - 5*z0^3 - 4/3*x0*x1*z1 
        + 1/3*x1*y0*z1 + 1/3*x0*y1*z1 + 2/3*y0*y1*z1 - 8/3*x1*z0*z1 + 2*y1*z0*z1 - 4/3*x0*z1^2 + y0*z1^2 - 5*z0*z1^2) 
of Multivariate Polynomial Ring in x0, x1, y0, y1, z0, z1 over Rational Field

We can check that the point p is still a root of all generators of J:

sage: [f.subs(x0=1,y0=2,z0=1,x1=0,y1=0,z1=0) for f in J.gens()]
[0, 0]

Note

Based on a Singular implementation by Michael Brickenstein

class sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_macaulay2_repr¶

An ideal in a multivariate polynomial ring, which has an underlying Macaulay2 ring associated to it.

EXAMPLES:

sage: R.<x,y,z,w> = PolynomialRing(ZZ, 4)
sage: I = ideal(x*y-z^2, y^2-w^2)
sage: I
Ideal (x*y - z^2, y^2 - w^2) of Multivariate Polynomial Ring in x, y, z, w over Integer Ring

class sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_magma_repr¶

class sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_singular_repr¶

An ideal in a multivariate polynomial ring, which has an underlying Singular ring associated to it.

associated_primes(*args, **kwds)¶

Return a list of the associated primes of primary ideals of which the intersection is $I$ = self.

An ideal $Q$ is called primary if it is a proper ideal of the ring $R$ and if whenever $ab \in Q$ and $a \not\in Q$ then $b^n \in Q$ for some $n \in \ZZ$ .

If $Q$ is a primary ideal of the ring $R$ , then the radical ideal $P$ of $Q$ , i.e. $P = \{a \in R, a^n \in Q\}$ for some $n \in \ZZ$ , is called the associated prime of $Q$ .

If $I$ is a proper ideal of the ring $R$ then there exists a decomposition in primary ideals $Q_i$ such that

their intersection is $I$
none of the $Q_i$ contains the intersection of the rest, and
the associated prime ideals of $Q_i$ are pairwise different.

This method returns the associated primes of the $Q_i$ .

INPUT:

algorithm - string:
'sy' - (default) use the shimoyama-yokoyama algorithm
'gtz' - use the gianni-trager-zacharias algorithm

OUTPUT:

list - a list of associated primes

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ, 3, order='lex')
sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y-z^2)*R
sage: pd = I.associated_primes(); pd
[Ideal (z^3 + 2, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field,
 Ideal (z^2 + 1, y + 1) of Multivariate Polynomial Ring in x, y, z over Rational Field]

ALGORITHM: Uses Singular.

REFERENCES:

Thomas Becker and Volker Weispfenning. Groebner Bases - A Computational Approach To Commutative Algebra. Springer, New York 1993.

basis_is_groebner(*args, **kwds)¶

Returns True if the generators of this ideal (self.gens()) form a Groebner basis.

Let $I$ be the set of generators of this ideal. The check is performed by trying to lift $Syz(LM(I))$ to $Syz(I)$ as $I$ forms a Groebner basis if and only if for every element $S$ in $Syz(LM(I))$ :

$S * G = \sum_{i=0}^{m} h_ig_i ---->_G 0.$

ALGORITHM: Uses Singular

EXAMPLE:

sage: R.<a,b,c,d,e,f,g,h,i,j> = PolynomialRing(GF(127),10)
sage: I = sage.rings.ideal.Cyclic(R,4)
sage: I.basis_is_groebner()
False
sage: I2 = Ideal(I.groebner_basis())
sage: I2.basis_is_groebner()
True

A more complicated example:

sage: R.<U6,U5,U4,U3,U2, u6,u5,u4,u3,u2, h> = PolynomialRing(GF(7583))
sage: l = [u6 + u5 + u4 + u3 + u2 - 3791*h, \
           U6 + U5 + U4 + U3 + U2 - 3791*h, \
           U2*u2 - h^2, U3*u3 - h^2, U4*u4 - h^2, \
           U5*u4 + U5*u3 + U4*u3 + U5*u2 + U4*u2 + U3*u2 - 3791*U5*h - 3791*U4*h - 3791*U3*h - 3791*U2*h - 2842*h^2, \
           U4*u5 + U3*u5 + U2*u5 + U3*u4 + U2*u4 + U2*u3 - 3791*u5*h - 3791*u4*h - 3791*u3*h - 3791*u2*h - 2842*h^2, \
           U5*u5 - h^2, U4*U2*u3 + U5*U3*u2 + U4*U3*u2 + U3^2*u2 - 3791*U5*U3*h - 3791*U4*U3*h - 3791*U3^2*h - 3791*U5*U2*h \
            - 3791*U4*U2*h + U3*U2*h - 3791*U2^2*h - 3791*U4*u3*h - 3791*U4*u2*h - 3791*U3*u2*h - 2843*U5*h^2 + 1897*U4*h^2 - 946*U3*h^2 - 947*U2*h^2 + 2370*h^3, \
           U3*u5*u4 + U2*u5*u4 + U3*u4^2 + U2*u4^2 + U2*u4*u3 - 3791*u5*u4*h - 3791*u4^2*h - 3791*u4*u3*h - 3791*u4*u2*h + u5*h^2 - 2842*u4*h^2, \
           U2*u5*u4*u3 + U2*u4^2*u3 + U2*u4*u3^2 - 3791*u5*u4*u3*h - 3791*u4^2*u3*h - 3791*u4*u3^2*h - 3791*u4*u3*u2*h + u5*u4*h^2 + u4^2*h^2 + u5*u3*h^2 - 2842*u4*u3*h^2, \
           U5^2*U4*u3 + U5*U4^2*u3 + U5^2*U4*u2 + U5*U4^2*u2 + U5^2*U3*u2 + 2*U5*U4*U3*u2 + U5*U3^2*u2 - 3791*U5^2*U4*h - 3791*U5*U4^2*h - 3791*U5^2*U3*h \
            + U5*U4*U3*h - 3791*U5*U3^2*h - 3791*U5^2*U2*h + U5*U4*U2*h + U5*U3*U2*h - 3791*U5*U2^2*h - 3791*U5*U3*u2*h - 2842*U5^2*h^2 + 1897*U5*U4*h^2 \
            - U4^2*h^2 - 947*U5*U3*h^2 - U4*U3*h^2 - 948*U5*U2*h^2 - U4*U2*h^2 - 1422*U5*h^3 + 3791*U4*h^3, \
           u5*u4*u3*u2*h + u4^2*u3*u2*h + u4*u3^2*u2*h + u4*u3*u2^2*h + 2*u5*u4*u3*h^2 + 2*u4^2*u3*h^2 + 2*u4*u3^2*h^2 + 2*u5*u4*u2*h^2 + 2*u4^2*u2*h^2 \
            + 2*u5*u3*u2*h^2 + 1899*u4*u3*u2*h^2, \
           U5^2*U4*U3*u2 + U5*U4^2*U3*u2 + U5*U4*U3^2*u2 - 3791*U5^2*U4*U3*h - 3791*U5*U4^2*U3*h - 3791*U5*U4*U3^2*h - 3791*U5*U4*U3*U2*h \
            + 3791*U5*U4*U3*u2*h + U5^2*U4*h^2 + U5*U4^2*h^2 + U5^2*U3*h^2 - U4^2*U3*h^2 - U5*U3^2*h^2 - U4*U3^2*h^2 - U5*U4*U2*h^2 \
            - U5*U3*U2*h^2 - U4*U3*U2*h^2 + 3791*U5*U4*h^3 + 3791*U5*U3*h^3 + 3791*U4*U3*h^3, \
           u4^2*u3*u2*h^2 + 1515*u5*u3^2*u2*h^2 + u4*u3^2*u2*h^2 + 1515*u5*u4*u2^2*h^2 + 1515*u5*u3*u2^2*h^2 + u4*u3*u2^2*h^2 \
            + 1521*u5*u4*u3*h^3 - 3028*u4^2*u3*h^3 - 3028*u4*u3^2*h^3 + 1521*u5*u4*u2*h^3 - 3028*u4^2*u2*h^3 + 1521*u5*u3*u2*h^3 + 3420*u4*u3*u2*h^3, \
           U5^2*U4*U3*U2*h + U5*U4^2*U3*U2*h + U5*U4*U3^2*U2*h + U5*U4*U3*U2^2*h + 2*U5^2*U4*U3*h^2 + 2*U5*U4^2*U3*h^2 + 2*U5*U4*U3^2*h^2 \
            + 2*U5^2*U4*U2*h^2 + 2*U5*U4^2*U2*h^2 + 2*U5^2*U3*U2*h^2 - 2*U4^2*U3*U2*h^2 - 2*U5*U3^2*U2*h^2 - 2*U4*U3^2*U2*h^2 \
             - 2*U5*U4*U2^2*h^2 - 2*U5*U3*U2^2*h^2 - 2*U4*U3*U2^2*h^2 - U5*U4*U3*h^3 - U5*U4*U2*h^3 - U5*U3*U2*h^3 - U4*U3*U2*h^3]

sage: Ideal(l).basis_is_groebner()
False
sage: gb = Ideal(l).groebner_basis()
sage: Ideal(gb).basis_is_groebner()
True

Note

From the Singular Manual for the reduce function we use in this method: ‘The result may have no meaning if the second argument (self) is not a standard basis’. I (malb) believe this refers to the mathematical fact that the results may have no meaning if self is no standard basis, i.e., Singular doesn’t ‘add’ any additional ‘nonsense’ to the result. So we may actually use reduce to determine if self is a Groebner basis.

complete_primary_decomposition(*args, **kwds)¶

Return a list of primary ideals and their associated primes such that the intersection of the primary ideal $Q_i$ is $I$ = self.

An ideal $Q$ is called primary if it is a proper ideal of the ring $R$ and if whenever $ab \in Q$ and $a \not\in Q$ then $b^n \in Q$ for some $n \in \ZZ$ .

If $Q$ is a primary ideal of the ring $R$ , then the radical ideal $P$ of $Q$ , i.e. $P = \{a \in R, a^n \in Q\}$ for some $n \in \ZZ$ , is called the associated prime of $Q$ .

If $I$ is a proper ideal of the ring $R$ then there exists a decomposition in primary ideals $Q_i$ such that

their intersection is $I$
none of the $Q_i$ contains the intersection of the rest, and
the associated prime ideals of $Q_i$ are pairwise different.

This method returns these $Q_i$ and their associated primes.

INPUT:

algorithm - string:
- 'sy' - (default) use the shimoyama-yokoyama algorithm
- 'gtz' - use the gianni-trager-zacharias algorithm

OUTPUT:

list - a list of primary ideals and their associated primes [(primary ideal, associated prime), ...]

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ, 3, order='lex')
sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y-z^2)*R
sage: pd = I.complete_primary_decomposition(); pd
[(Ideal (z^6 + 4*z^3 + 4, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field,
  Ideal (z^3 + 2, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field),
 (Ideal (z^2 + 1, y + 1) of Multivariate Polynomial Ring in x, y, z over Rational Field,
  Ideal (z^2 + 1, y + 1) of Multivariate Polynomial Ring in x, y, z over Rational Field)]

sage: I.complete_primary_decomposition(algorithm = 'gtz')
[(Ideal (z^6 + 4*z^3 + 4, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field,
  Ideal (z^3 + 2, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field),
 (Ideal (z^2 + 1, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field,
  Ideal (z^2 + 1, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field)]

sage: reduce(lambda Qi,Qj: Qi.intersection(Qj), [Qi for (Qi,radQi) in pd]) == I
True

sage: [Qi.radical() == radQi for (Qi,radQi) in pd]
[True, True]

sage: P.<x,y,z> = PolynomialRing(ZZ)
sage: I = ideal( x^2 - 3*y, y^3 - x*y, z^3 - x, x^4 - y*z + 1 )
sage: I.complete_primary_decomposition()
...
ValueError: Coefficient ring must be a field for function 'complete_primary_decomposition'.

ALGORITHM: Uses Singular.

Note

See [BW93] for an introduction to primary decomposition.

dimension(*args, **kwds)¶

The dimension of the ring modulo this ideal.

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(GF(32003),order='degrevlex')
sage: I = ideal(x^2-y,x^3)
sage: I.dimension()
1

For polynomials over a finite field of order too large for Singular, this falls back on a toy implementation of Buchberger to compute the Groebner basis, then uses the algorithm described in Chapter 9, Section 1 of Cox, Little, and O’Shea’s “Ideals, Varieties, and Algorithms”.

EXAMPLE:

sage: R.<x,y> = PolynomialRing(GF(2147483659),order='lex')
sage: I = R.ideal([x*y,x*y+1])
sage: I.dimension()
verbose 0 (...: multi_polynomial_ideal.py, dimension) Warning: falling back to very slow toy implementation.
0
sage: I=ideal([x*(x*y+1),y*(x*y+1)])
sage: I.dimension()
verbose 0 (...: multi_polynomial_ideal.py, dimension) Warning: falling back to very slow toy implementation.
1
sage: I = R.ideal([x^3*y,x*y^2])
sage: I.dimension()
verbose 0 (...: multi_polynomial_ideal.py, dimension) Warning: falling back to very slow toy implementation.
1
sage: R.<x,y> = PolynomialRing(GF(2147483659),order='lex')
sage: I = R.ideal(0)
sage: I.dimension()
verbose 0 (...: multi_polynomial_ideal.py, dimension) Warning: falling back to very slow toy implementation.
2

ALGORITHM: Uses Singular, unless the characteristic is too large.

Note

Requires computation of a Groebner basis, which can be a very expensive operation.

elimination_ideal(*args, **kwds)¶

Returns the elimination ideal this ideal with respect to the variables given in variables.

INPUT:

variables - a list or tuple of variables in self.ring()

EXAMPLE:

sage: R.<x,y,t,s,z> = PolynomialRing(QQ,5)
sage: I = R * [x-t,y-t^2,z-t^3,s-x+y^3]
sage: I.elimination_ideal([t,s])
Ideal (y^2 - x*z, x*y - z, x^2 - y) of Multivariate
Polynomial Ring in x, y, t, s, z over Rational Field

ALGORITHM: Uses SINGULAR

Note

Requires computation of a Groebner basis, which can be a very expensive operation.

genus(*args, **kwds)¶

Return the genus of the projective curve defined by this ideal, which must be 1 dimensional.

EXAMPLE:

Consider the hyperelliptic curve $y^2 = 4x^5 - 30x^3 + 45x - 22$ over $\QQ$ , it has genus 2:

sage: P, x = PolynomialRing(QQ,"x").objgen()
sage: f = 4*x^5 - 30*x^3 + 45*x - 22
sage: C = HyperellipticCurve(f); C
Hyperelliptic Curve over Rational Field defined by y^2 = 4*x^5 - 30*x^3 + 45*x - 22
sage: C.genus()
2

sage: P.<x,y> = PolynomialRing(QQ)
sage: f = y^2 - 4*x^5 - 30*x^3 + 45*x - 22
sage: I = Ideal([f])
sage: I.genus()
2

hilbert_polynomial(*args, **kwds)¶

Return the Hilbert polynomial of this ideal.

Let $I$ = self be a homogeneous ideal and $R$ = self.ring() be a graded commutative algebra ( $R = \oplus R_d$ ) over a field $K$ . The Hilbert polynomial is the unique polynomial $HP(t)$ with rational coefficients such that $HP(d) = dim_K R_d$ for all but finitely many positive integers $d$ .

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(QQ)
sage: I = Ideal([x^3*y^2 + 3*x^2*y^2*z + y^3*z^2 + z^5])
sage: I.hilbert_polynomial()
5*t - 5

hilbert_series(*args, **kwds)¶

Return the Hilbert series of this ideal.

Let $I$ = self be a homogeneous ideal and $R$ = self.ring() be a graded commutative algebra ( $R = \oplus R_d$ ) over a field $K$ . Then the Hilbert function is defined as $H(d) = dim_K R_d$ and the Hilbert series of $I$ is defined as the formal power series $HS(t) = \sum_0^{\infty} H(d) t^d$ .

This power series can be expressed as $HS(t) = Q(t)/(1-t)^n$ where $Q(t)$ is a polynomial over $Z$ and $n$ the number of variables in $R$ . This method returns $Q(t)/(1-t)^n$ .

EXAMPLE:

sage: P.<x,y,z> = PolynomialRing(QQ)
sage: I = Ideal([x^3*y^2 + 3*x^2*y^2*z + y^3*z^2 + z^5])
sage: I.hilbert_series()
(-t^4 - t^3 - t^2 - t - 1)/(-t^2 + 2*t - 1)

integral_closure(*args, **kwds)¶

Let $I$ = self.

Returns the integral closure of $I, ..., I^p$ , where $sI$ is an ideal in the polynomial ring $R=k[x(1),...x(n)]$ . If $p$ is not given, or $p=0$ , compute the closure of all powers up to the maximum degree in t occurring in the closure of $R[It]$ (so this is the last power whose closure is not just the sum/product of the smaller). If $r$ is given and r is True, I.integral_closure() starts with a check whether I is already a radical ideal.

INPUT:

p - powers of I (default: 0)
r - check whether self is a radical ideal first (default: True)

EXAMPLE:

sage: R.<x,y> = QQ[]
sage: I = ideal([x^2,x*y^4,y^5])
sage: I.integral_closure()
[x^2, y^5, -x*y^3]

ALGORITHM: Use Singular

interreduced_basis(*args, **kwds)¶

If this ideal is spanned by $(f_1, ..., f_n)$ this method returns $(g_1, ..., g_s)$ such that:

$(f_1,...,f_n) = (g_1,...,g_s)$
$LT(g_i) != LT(g_j)$ for all $i != j$
$LT(g_i)$ does not divide $m$ for all monomials $m$ of

$\{g_1,...,g_{i-1},g_{i+1},...,g_s\}$
$LC(g_i) == 1$ for all $i$ if the coefficient ring is a field.

EXAMPLE:

sage: R.<x,y,z> = PolynomialRing(QQ)
sage: I = Ideal([z*x+y^3,z+y^3,z+x*y])
sage: I.interreduced_basis()
[y^3 + z, x*y + z, x*z - z] 

Note that tail reduction for local orderings is not well-defined:

sage: R.<x,y,z> = PolynomialRing(QQ,order='negdegrevlex')
sage: I = Ideal([z*x+y^3,z+y^3,z+x*y])
sage: I.interreduced_basis()
[z + x*y, x*y - y^3, x^2*y - y^3]

A fixed error with nonstandard base fields:

sage: R.<t>=QQ['t']
sage: K.<x,y>=R.fraction_field()['x,y']
sage: I=t*x*K
sage: I.interreduced_basis()
[x]

ALGORITHM: Uses Singular’s interred command or sage.rings.polynomial.toy_buchberger.inter_reduction`() if conversion to Singular fails.

intersection(*args, **kwds)¶

Return the intersection of the two ideals.

EXAMPLES:

sage: R.<x,y> = PolynomialRing(QQ, 2, order='lex')
sage: I = x*R
sage: J = y*R
sage: I.intersection(J)
Ideal (x*y) of Multivariate Polynomial Ring in x, y over Rational Field

The following simple example illustrates that the product need not equal the intersection.

sage: I = (x^2, y)*R
sage: J = (y^2, x)*R
sage: K = I.intersection(J); K
Ideal (y^2, x*y, x^2) of Multivariate Polynomial Ring in x, y over Rational Field
sage: IJ = I*J; IJ
Ideal (x^2*y^2, x^3, y^3, x*y) of Multivariate Polynomial Ring in x, y over Rational Field
sage: IJ == K
False

minimal_associated_primes(*args, **kwds)¶

OUTPUT:

list - a list of prime ideals

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ, 3, 'xyz')
sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y-z^2)*R
sage: I.minimal_associated_primes ()
[Ideal (z^2 + 1, -z^2 + y) of Multivariate Polynomial Ring
in x, y, z over Rational Field, Ideal (z^3 + 2, -z^2 + y)
of Multivariate Polynomial Ring in x, y, z over Rational
Field]

ALGORITHM: Uses Singular.

plot(singular=Singular)¶

If you somehow manage to install surf, perhaps you can use this function to implicitly plot the real zero locus of this ideal (if principal).

INPUT:

self - must be a principal ideal in 2 or 3 vars over QQ.

EXAMPLES:

Implicit plotting in 2-d:

sage: R.<x,y> = PolynomialRing(QQ,2)
sage: I = R.ideal([y^3 - x^2])
sage: I.plot()        # cusp
sage: I = R.ideal([y^2 - x^2 - 1])
sage: I.plot()        # hyperbola 
sage: I = R.ideal([y^2 + x^2*(1/4) - 1])
sage: I.plot()        # ellipse
sage: I = R.ideal([y^2-(x^2-1)*(x-2)])
sage: I.plot()        # elliptic curve

Implicit plotting in 3-d:

sage: R.<x,y,z> = PolynomialRing(QQ,3)
sage: I = R.ideal([y^2 + x^2*(1/4) - z])
sage: I.plot()          # a cone         optional - surf
sage: I = R.ideal([y^2 + z^2*(1/4) - x])
sage: I.plot()          # same code, from a different angle  optional - surf
sage: I = R.ideal([x^2*y^2+x^2*z^2+y^2*z^2-16*x*y*z])
sage: I.plot()          # Steiner surface   optional - surf

AUTHORS:

David Joyner (2006-02-12)

primary_decomposition(*args, **kwds)¶

Return a list of primary ideals such that their intersection is $I$ = self.

An ideal $Q$ is called primary if it is a proper ideal of the ring $R$ and if whenever $ab \in Q$ and $a \not\in Q$ then $b^n \in Q$ for some $n \in \ZZ$ .

If $I$ is a proper ideal of the ring $R$ then there exists a decomposition in primary ideals $Q_i$ such that

their intersection is $I$
none of the $Q_i$ contains the intersection of the rest, and
the associated prime ideals of $Q_i$ are pairwise different.

This method returns these $Q_i$ .

INPUT:

algorithm - string:
'sy' - (default) use the shimoyama-yokoyama algorithm

'gtz' - use the gianni-trager-zacharias algorithm

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ, 3, order='lex')
sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y-z^2)*R
sage: pd = I.primary_decomposition(); pd
[Ideal (z^6 + 4*z^3 + 4, y - z^2) of Multivariate Polynomial Ring in x, y, z over Rational Field,
 Ideal (z^2 + 1, y + 1) of Multivariate Polynomial Ring in x, y, z over Rational Field]

sage: reduce(lambda Qi,Qj: Qi.intersection(Qj), pd) == I
True

ALGORITHM: Uses Singular.

REFERENCES:

Thomas Becker and Volker Weispfenning. Groebner Bases - A Computational Approach To Commutative Algebra. Springer, New York 1993.

quotient(*args, **kwds)¶

Given ideals $I$ = self and $J$ in the same polynomial ring $P$ , return the ideal quotient of $I$ by $J$ consisting of the polynomials $a$ of $P$ such that $\{aJ \subset I\}$ .

This is also referred to as the colon ideal ( $I$ : $J$ ).

INPUT:

J - multivariate polynomial ideal

EXAMPLE:

sage: R.<x,y,z> = PolynomialRing(GF(181),3)
sage: I = Ideal([x^2+x*y*z,y^2-z^3*y,z^3+y^5*x*z])
sage: J = Ideal([x])
sage: Q = I.quotient(J)
sage: y*z + x in I
False
sage: x in J
True
sage: x * (y*z + x) in I
True

radical(*args, **kwds)¶

The radical of this ideal.

EXAMPLES:

This is an obviously not radical ideal:

sage: R.<x,y,z> = PolynomialRing(QQ, 3)
sage: I = (x^2, y^3, (x*z)^4 + y^3 + 10*x^2)*R
sage: I.radical()
Ideal (y, x) of Multivariate Polynomial Ring in x, y, z over Rational Field

That the radical is correct is clear from the Groebner basis.

sage: I.groebner_basis()
[y^3, x^2]

This is the example from the Singular manual:

sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y-z^2)*R
sage: I.radical()
Ideal (z^2 - y, y^2*z + y*z + 2*y + 2) of Multivariate Polynomial Ring in x, y, z over Rational Field

Note

From the Singular manual: A combination of the algorithms of Krick/Logar and Kemper is used. Works also in positive characteristic (Kempers algorithm).

sage: R.<x,y,z> = PolynomialRing(GF(37), 3)
sage: p = z^2 + 1; q = z^3 + 2
sage: I = (p*q^2, y - z^2)*R
sage: I.radical()
Ideal (z^2 - y, y^2*z + y*z + 2*y + 2) of Multivariate Polynomial Ring in x, y, z over Finite Field of size 37

reduced_basis(*args, **kwds)¶

Warning

This function is deprecated. It will be removed in a future release of Sage. Please use the interreduced_basis() function instead.

If this ideal is spanned by $(f_1, ..., f_n)$ this method returns $(g_1, ..., g_s)$ such that:

$(f_1,...,f_n) = (g_1,...,g_s)$
$LT(g_i) != LT(g_j)$ for all $i != j$
$LT(g_i)$ does not divide $m$ for all monomials $m$ of $\{g_1,...,g_{i-1},g_{i+1},...,g_s\}$
$LC(g_i) == 1$ for all $i$ .

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ)
sage: I = Ideal([z*x+y^3,z+y^3,z+x*y])
sage: I.reduced_basis()
doctest:...: DeprecationWarning: This function is deprecated. It will be removed in a future release of Sage. Please use the interreduced_basis() function instead.
[y^3 + z, x*y + z, x*z - z] 

sage: R.<x,y,z> = PolynomialRing(QQ,order='negdegrevlex')
sage: I = Ideal([z*x+y^3,z+y^3,z+x*y])
sage: I.reduced_basis()
[z + x*y, x*y - y^3, x^2*y - y^3]

ALGORITHM:

Uses Singular’s interred command or toy_buchberger.inter_reduction if conversion to Singular fails.

syzygy_module(*args, **kwds)¶

Computes the first syzygy (i.e., the module of relations of the given generators) of the ideal.

EXAMPLE:

sage: R.<x,y> = PolynomialRing(QQ)
sage: f = 2*x^2 + y
sage: g = y
sage: h = 2*f + g
sage: I = Ideal([f,g,h])
sage: M = I.syzygy_module(); M
[       -2        -1         1]
[       -y 2*x^2 + y         0]
sage: G = vector(I.gens())
sage: M*G
(0, 0)

ALGORITHM: Uses Singular’s syz command

transformed_basis(*args, **kwds)¶

Returns a lex or other_ring Groebner Basis for this ideal.

INPUT:

algorithm - see below for options.
other_ring - only valid for algorithm ‘fglm’, if

provided conversion will be performed to this ring. Otherwise a lex Groebner basis will be returned.

ALGORITHMS:

fglm: FGLM algorithm. The input ideal must be given with a reduced Groebner Basis of a zero-dimensional ideal
gwalk: Groebner Walk algorithm (default)
awalk1: ‘first alternative’ algorithm
awalk2: ‘second alternative’ algorithm
twalk: Tran algorithm
fwalk: Fractal Walk algorithm

EXAMPLES:

sage: R.<x,y,z> = PolynomialRing(QQ,3)
sage: I = Ideal([y^3+x^2,x^2*y+x^2, x^3-x^2, z^4-x^2-y])
sage: I = Ideal(I.groebner_basis())
sage: S.<z,x,y> = PolynomialRing(QQ,3,order='lex')
sage: J = Ideal(I.transformed_basis('fglm',S))
sage: J
Ideal (z^4 + y^3 - y, x^2 + y^3, x*y^3 - y^3, y^4 + y^3)
 of Multivariate Polynomial Ring in z, x, y over Rational Field

sage: R.<z,y,x>=PolynomialRing(GF(32003),3,order='lex')
sage: I=Ideal([y^3+x*y*z+y^2*z+x*z^3,3+x*y+x^2*y+y^2*z]) 
sage: I.transformed_basis('gwalk')
[z*y^2 + y*x^2 + y*x + 3, 
 z*x + 8297*y^8*x^2 + 8297*y^8*x + 3556*y^7 - 8297*y^6*x^4 + 15409*y^6*x^3 - 8297*y^6*x^2 
 - 8297*y^5*x^5 + 15409*y^5*x^4 - 8297*y^5*x^3 + 3556*y^5*x^2 + 3556*y^5*x + 3556*y^4*x^3 
 + 3556*y^4*x^2 - 10668*y^4 - 10668*y^3*x - 8297*y^2*x^9 - 1185*y^2*x^8 + 14224*y^2*x^7 
 - 1185*y^2*x^6 - 8297*y^2*x^5 - 14223*y*x^7 - 10666*y*x^6 - 10666*y*x^5 - 14223*y*x^4 
 + x^5 + 2*x^4 + x^3, 
 y^9 - y^7*x^2 - y^7*x - y^6*x^3 - y^6*x^2 - 3*y^6 - 3*y^5*x - y^3*x^7 - 3*y^3*x^6 
 - 3*y^3*x^5 - y^3*x^4 - 9*y^2*x^5 - 18*y^2*x^4 - 9*y^2*x^3 - 27*y*x^3 - 27*y*x^2 - 27*x]

ALGORITHM: Uses Singular

triangular_decomposition(*args, **kwds)¶

Decompose zero-dimensional ideal self into triangular sets.

This requires that the given basis is reduced w.r.t. to the lexicographical monomial ordering. If the basis of self does not have this property, the required Groebner basis is computed implicitly.

INPUT:

algorithm - string or None (default: None)

ALGORITHMS:

singular:triangL - decomposition of self into triangular systems (Lazard).
singular:triangLfak - decomp. of self into tri. systems plus factorization.
- singular:triangM - decomposition of self into triangular systems (Moeller).

OUTPUT: a list $T$ of lists $t$ such that the variety of self is the union of the varieties of $t$ in $L$ and each $t$ is in triangular form.

EXAMPLE:

sage: P.<e,d,c,b,a> = PolynomialRing(QQ,5,order='lex')
sage: I = sage.rings.ideal.Cyclic(P)
sage: GB = Ideal(I.groebner_basis('libsingular:stdfglm'))
sage: GB.triangular_decomposition('singular:triangLfak')
[Ideal (a - 1, b - 1, c - 1, d^2 + 3*d + 1, e + d + 3) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a - 1, b - 1, c^2 + 3*c + 1, d + c + 3, e - 1) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a - 1, b^2 + 3*b + 1, c + b + 3, d - 1, e - 1) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a - 1, b^4 + b^3 + b^2 + b + 1, c - b^2, d - b^3, e + b^3 + b^2 + b + 1) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^2 + 3*a + 1, b - 1, c - 1, d - 1, e + a + 3) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^2 + 3*a + 1, b + a + 3, c - 1, d - 1, e - 1) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 - 4*a^3 + 6*a^2 + a + 1, 11*b^2 - 6*b*a^3 + 26*b*a^2 - 41*b*a + 4*b + 8*a^3 - 31*a^2 + 40*a + 24, 11*c + 3*a^3 - 13*a^2 + 26*a - 2, 11*d + 3*a^3 - 13*a^2 + 26*a - 2, 11*e + 11*b - 6*a^3 + 26*a^2 - 41*a + 4) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + a^2 + a + 1, b - 1, c + a^3 + a^2 + a + 1, d - a^3, e - a^2) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + a^2 + a + 1, b - a, c - a, d^2 + 3*d*a + a^2, e + d + 3*a) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + a^2 + a + 1, b - a, c^2 + 3*c*a + a^2, d + c + 3*a, e - a) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + a^2 + a + 1, b^2 + 3*b*a + a^2, c + b + 3*a, d - a, e - a) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + a^2 + a + 1, b^3 + b^2*a + b^2 + b*a^2 + b*a + b + a^3 + a^2 + a + 1, c + b^2*a^3 + b^2*a^2 + b^2*a + b^2, d - b^2*a^2 - b^2*a - b^2 - b*a^2 - b*a - a^2, e - b^2*a^3 + b*a^2 + b*a + b + a^2 + a) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field, 
Ideal (a^4 + a^3 + 6*a^2 - 4*a + 1, 11*b^2 - 6*b*a^3 - 10*b*a^2 - 39*b*a - 2*b - 16*a^3 - 23*a^2 - 104*a + 24, 11*c + 3*a^3 + 5*a^2 + 25*a + 1, 11*d + 3*a^3 + 5*a^2 + 25*a + 1, 11*e + 11*b - 6*a^3 - 10*a^2 - 39*a - 2) of Multivariate Polynomial Ring in e, d, c, b, a over Rational Field]

sage: R.<x1,x2> = PolynomialRing(QQ, 2, order='lex')
sage: f1 = 1/2*((x1^2 + 2*x1 - 4)*x2^2 + 2*(x1^2 + x1)*x2 + x1^2)
sage: f2 = 1/2*((x1^2 + 2*x1 + 1)*x2^2 + 2*(x1^2 + x1)*x2 - 4*x1^2)
sage: I = Ideal(f1,f2)
sage: I.triangular_decomposition()
[Ideal (x2, x1^2) of Multivariate Polynomial Ring in x1, x2 over Rational Field, 
 Ideal (x2, x1^2) of Multivariate Polynomial Ring in x1, x2 over Rational Field, 
 Ideal (x2, x1^2) of Multivariate Polynomial Ring in x1, x2 over Rational Field, 
 Ideal (x2^4 + 4*x2^3 - 6*x2^2 - 20*x2 + 5, 8*x1 - x2^3 + x2^2 + 13*x2 - 5) of Multivariate Polynomial Ring in x1, x2 over Rational Field]

variety(*args, **kwds)¶

Return the variety of self.

Given a zero-dimensional ideal $I$ (== self) of a polynomial ring P whose order is lexicographic, return the variety of I as a list of dictionaries with (variable, value) pairs. By default, the variety of the ideal over its coefficient field $K$ is returned; ring can be specified to find the variety over a different ring.

These dictionaries have cardinality equal to the number of variables in P and represent assignments of values to these variables such that all polynomials in I vanish.

If ring is specified, then a triangular decomposition of self is found over the original coefficient field $K$ ; then the triangular systems are solved using root-finding over ring. This is particularly useful when $K$ is QQ (to allow fast symbolic computation of the triangular decomposition) and ring is RR, AA, CC, or QQbar (to compute the whole real or complex variety of the ideal).

Note that with ring``=``RR or CC, computation is done numerically and potentially inaccurately; in particular, the number of points in the real variety may be miscomputed. With ring``=``AA or QQbar, computation is done exactly (which may be much slower, of course).

INPUT:

ring - return roots in the ring instead of the base ring of this ideal (default: None)
proof - return a provably correct result (default: True)

EXAMPLE:

sage: K.<w> = GF(27) # this example is from the MAGMA handbook
sage: P.<x, y> = PolynomialRing(K, 2, order='lex')
sage: I = Ideal([ x^8 + y + 2, y^6 + x*y^5 + x^2 ])
sage: I = Ideal(I.groebner_basis()); I
Ideal (x - y^47 - y^45 + y^44 - y^43 + y^41 - y^39 - y^38
- y^37 - y^36 + y^35 - y^34 - y^33 + y^32 - y^31 + y^30 +
y^28 + y^27 + y^26 + y^25 - y^23 + y^22 + y^21 - y^19 -
y^18 - y^16 + y^15 + y^13 + y^12 - y^10 + y^9 + y^8 + y^7
- y^6 + y^4 + y^3 + y^2 + y - 1, y^48 + y^41 - y^40 + y^37
- y^36 - y^33 + y^32 - y^29 + y^28 - y^25 + y^24 + y^2 + y
+ 1) of Multivariate Polynomial Ring in x, y over Finite
Field in w of size 3^3

sage: V = I.variety(); V
[{y: w^2 + 2, x: 2*w}, {y: w^2 + w, x: 2*w + 1}, {y: w^2 + 2*w, x: 2*w + 2}]

sage: [f.subs(v) for f in I.gens() for v in V] # check that all polynomials vanish
[0, 0, 0, 0, 0, 0]

However, we only account for solutions in the ground field and not in the algebraic closure:

sage: I.vector_space_dimension() 
48

Here we compute the points of intersection of a hyperbola and a circle, in several fields:

sage: K.<x, y> = PolynomialRing(QQ, 2, order='lex')
sage: I = Ideal([ x*y - 1, (x-2)^2 + (y-1)^2 - 1])
sage: I = Ideal(I.groebner_basis()); I
Ideal (x + y^3 - 2*y^2 + 4*y - 4, y^4 - 2*y^3 + 4*y^2 - 4*y + 1)
of Multivariate Polynomial Ring in x, y over Rational Field

These two curves have one rational intersection:

sage: I.variety()
[{y: 1, x: 1}]

There are two real intersections:

sage: I.variety(ring=RR)
[{y: 0.361103080528647, x: 2.76929235423863},
 {y: 1.00000000000000, x: 1.00000000000000}]
sage: I.variety(ring=AA)
[{x: 2.769292354238632?, y: 0.3611030805286474?}, 
 {x: 1, y: 1}]

and a total of four intersections:

sage: I.variety(ring=CC)
[{y: 0.31944845973567... - 1.6331702409152...*I,
  x: 0.11535382288068... + 0.58974280502220...*I},
 {y: 0.31944845973567... + 1.6331702409152...*I,
  x: 0.11535382288068... - 0.58974280502220...*I},
 {y: 0.36110308052864..., x: 2.7692923542386...},
 {y: 1.00000000000000, x: 1.00000000000000}]
sage: I.variety(ring=QQbar)
[{y: 0.3194484597356763? - 1.633170240915238?*I, 
  x: 0.11535382288068429? + 0.5897428050222055?*I},
 {y: 0.3194484597356763? + 1.633170240915238?*I, 
  x: 0.11535382288068429? - 0.5897428050222055?*I}, 
 {y: 0.3611030805286474?, x: 2.769292354238632?}, 
 {y: 1, x: 1}]

Computation over floating point numbers may compute only a partial solution, or even none at all. Notice that x values are missing from the following variety:

sage: R.<x,y> = CC[]
sage: I = ideal([x^2+y^2-1,x*y-1])
sage: I.variety()
verbose 0 (...: multi_polynomial_ideal.py, variety) Warning: computations in the complex field are inexact; variety may be computed partially or incorrectly.
verbose 0 (...: multi_polynomial_ideal.py, variety) Warning: falling back to very slow toy implementation.
[{y: -0.86602540378443... - 0.500000000000000*I}, 
 {y: -0.86602540378443... + 0.500000000000000*I}, 
 {y: 0.86602540378443... - 0.500000000000000*I}, 
 {y: 0.86602540378443... + 0.500000000000000*I}]

This is due to precision error, which causes the computation of an intermediate Groebner basis to fail.

If the ground field’s characteristic is too large for Singular, we resort to a toy implementation:

sage: R.<x,y> = PolynomialRing(GF(2147483659),order='lex')
sage: I=ideal([x^3-2*y^2,3*x+y^4])
sage: I.variety()
verbose 0 (...: multi_polynomial_ideal.py, groebner_basis) Warning: falling back to very slow toy implementation.
verbose 0 (...: multi_polynomial_ideal.py, dimension) Warning: falling back to very slow toy implementation.
verbose 0 (...: multi_polynomial_ideal.py, variety) Warning: falling back to very slow toy implementation.
[{y: 0, x: 0}]

TESTS:

sage: K.<w> = GF(27)
sage: P.<x, y> = PolynomialRing(K, 2, order='lex')
sage: I = Ideal([ x^8 + y + 2, y^6 + x*y^5 + x^2 ])

Testing the robustness of the Singular interface

sage: T = I.triangular_decomposition('singular:triangLfak')
sage: I.variety()
[{y: w^2 + 2, x: 2*w}, {y: w^2 + w, x: 2*w + 1}, {y: w^2 + 2*w, x: 2*w + 2}]

Testing that a bug is indeed fixed.

sage: R = PolynomialRing(GF(2), 30, ['x%d'%(i+1) for i in range(30)], order='lex')
sage: R.inject_variables()
Defining...
sage: I = Ideal([x1 + 1, x2, x3 + 1, x5*x10 + x10 + x18, x5*x11 + x11, \
                 x5*x18, x6, x7 + 1, x9, x10*x11 + x10 + x18, x10*x18 + x18, \
                 x11*x18, x12, x13, x14, x15, x16 + 1, x17 + x18 + 1, x19, x20, \ 
                 x21 + 1, x22, x23, x24, x25 + 1, x28 + 1, x29 + 1, x30, x8, \
                 x26, x1^2 + x1, x2^2 + x2, x3^2 + x3, x4^2 + x4, x5^2 + x5, \
                 x6^2 + x6, x7^2 + x7, x8^2 + x8, x9^2 + x9, x10^2 + x10, \
                 x11^2 + x11, x12^2 + x12, x13^2 + x13, x14^2 + x14, x15^2 + x15, \
                 x16^2 + x16, x17^2 + x17, x18^2 + x18, x19^2 + x19, x20^2 + x20, \
                 x21^2 + x21, x22^2 + x22, x23^2 + x23, x24^2 + x24, x25^2 + x25, \
                 x26^2 + x26, x27^2 + x27, x28^2 + x28, x29^2 + x29, x30^2 + x30])
sage: I.basis_is_groebner()
True
sage: for V in I.variety():
...     print V
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 0, x19: 0, x18: 1, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 0, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 1, x19: 0, x18: 1, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 0, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 0, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 0, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 0, x19: 0, x18: 0, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 1, x4: 1, x19: 0, x18: 0, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 1, x25: 1, x9: 0, x8: 0, x20: 0, x17: 1, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 0, x19: 0, x18: 1, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 0, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}
{x14: 0, x24: 0, x16: 1, x1: 1, x3: 1, x2: 0, x5: 0, x4: 1, x19: 0, x18: 1, x7: 1, x6: 0, x10: 1, x30: 0, x28: 1, x29: 1, x13: 0, x27: 1, x11: 0, x25: 1, x9: 0, x8: 0, x20: 0, x17: 0, x23: 0, x26: 0, x15: 0, x21: 1, x12: 0, x22: 0}

Check that the issue at trac 7425 is fixed:

sage: R.<x, y, z> = QQ[]
sage: I = R.ideal([x^2-y^3*z, x+y*z])
sage: I.dimension()
1
sage: I.variety()
...
ValueError: The dimension of the ideal is 1, but it should be 0

ALGORITHM: Uses triangular decomposition.

vector_space_dimension(*args, **kwds)¶

Return the vector space dimension of the ring modulo this ideal. If the ideal is not zero-dimensional, a TypeError is raised.

ALGORITHM: Uses Singular.

EXAMPLE:

sage: R.<u,v> = PolynomialRing(QQ)
sage: g = u^4 + v^4 + u^3 + v^3
sage: I = ideal(g) + ideal(g.gradient())
sage: I.dimension()
0
sage: I.vector_space_dimension()
4

class sage.rings.polynomial.multi_polynomial_ideal.RedSBContext(singular=Singular)¶

Within this context all Singular Groebner basis calculations are reduced automatically.

AUTHORS:

Martin Albrecht

class sage.rings.polynomial.multi_polynomial_ideal.RequireField(f)¶

Bases: sage.misc.method_decorator.MethodDecorator

Decorator which throws an exception if a computation over a coefficient ring which is not a field is attempted.

Note

This decorator is used automatically internally so the user does not need to use it manually.

sage.rings.polynomial.multi_polynomial_ideal.is_MPolynomialIdeal(x)¶

Return True if the provided argument x is an ideal in the multivariate polynomial ring.

INPUT:

x - an arbitrary object

EXAMPLES:

sage: from sage.rings.polynomial.all import is_MPolynomialIdeal
sage: P.<x,y,z> = PolynomialRing(QQ)
sage: I = [x + 2*y + 2*z - 1, x^2 + 2*y^2 + 2*z^2 - x, 2*x*y + 2*y*z - y]

Sage distinguishes between a list of generators for an ideal and the ideal itself. This distinction is inconsistent with Singular but matches Magma’s behavior.

sage: is_MPolynomialIdeal(I)
False

sage: I = Ideal(I)
sage: is_MPolynomialIdeal(I)
True

sage.rings.polynomial.multi_polynomial_ideal.redSB(func)¶

Decorator to force a reduced Singular groebner basis.

TESTS:

sage: P.<a,b,c,d,e> = PolynomialRing(GF(127))
sage: J = sage.rings.ideal.Cyclic(P).homogenize()
sage: from sage.misc.sageinspect import sage_getsource
sage: "buchberger" in sage_getsource(J.interreduced_basis)
True

Note

This decorator is used automatically internally so the user does not need to use it manually.

sage.rings.polynomial.multi_polynomial_ideal.require_field¶: alias of RequireField

Ideals in multivariate polynomial rings.¶

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