# Compute Hilbert series of monomial ideals¶

This implementation was provided at trac ticket #26243 and is supposed to be a way out when Singular fails with an int overflow, which will regularly be the case in any example with more than 34 variables.

class sage.rings.polynomial.hilbert.Node

Bases: object

A node of a binary tree

It has slots for data that allow to recursively compute the first Hilbert series of a monomial ideal.

sage.rings.polynomial.hilbert.first_hilbert_series(I, grading=None, return_grading=False)

Return the first Hilbert series of the given monomial ideal.

INPUT:

• I – a monomial ideal (possibly defined in singular)
• grading – (optional) a list or tuple of integers used as degree weights
• return_grading – (default: False) whether to return the grading

OUTPUT:

A univariate polynomial, namely the first Hilbert function of I, and if return_grading==True also the grading used to compute the series.

EXAMPLES:

sage: from sage.rings.polynomial.hilbert import first_hilbert_series
sage: R = singular.ring(0,'(x,y,z)','dp')
sage: I = singular.ideal(['x^2','y^2','z^2'])
sage: first_hilbert_series(I)
-t^6 + 3*t^4 - 3*t^2 + 1
(-t^6 + 3*t^4 - 3*t^2 + 1, (1, 1, 1))
-t^12 + t^10 + t^8 - t^4 - t^2 + 1

sage.rings.polynomial.hilbert.hilbert_poincare_series(I, grading=None)

Return the Hilbert Poincaré series of the given monomial ideal.

INPUT:

• I – a monomial ideal (possibly defined in Singular)
• grading – (optional) a tuple of degree weights

EXAMPLES:

sage: from sage.rings.polynomial.hilbert import hilbert_poincare_series
sage: R = PolynomialRing(QQ,'x',9)
sage: I = [m.lm() for m in ((matrix(R,3,R.gens())^2).list()*R).groebner_basis()]*R
sage: hilbert_poincare_series(I)
(t^7 - 3*t^6 + 2*t^5 + 2*t^4 - 2*t^3 + 6*t^2 + 5*t + 1)/(t^4 - 4*t^3 + 6*t^2 - 4*t + 1)
t^9 + t^8 + t^7 + t^6 + t^5 + t^4 + t^3 + t^2 + t + 1


The following example is taken from trac ticket #20145:

sage: n=4;m=11;P = PolynomialRing(QQ,n*m,"x"); x = P.gens(); M = Matrix(n,x)
sage: from sage.rings.polynomial.hilbert import first_hilbert_series
sage: I = P.ideal(M.minors(2))
sage: J = P*[m.lm() for m in I.groebner_basis()]
sage: hilbert_poincare_series(J).numerator()
120*t^3 + 135*t^2 + 30*t + 1
sage: hilbert_poincare_series(J).denominator().factor()
(t - 1)^14


This example exceeds the current capabilities of Singular:

sage: J.hilbert_numerator(algorithm='singular')
Traceback (most recent call last):
...
RuntimeError: error in Singular function call 'hilb':
int overflow in hilb 1