SymmetricDivisorM0nbar -- the class of S_n symmetric divisors on the moduli space of stable n-pointed genus 0 curves

Description

This type implements S_n symmetric divisors on the moduli space of stable n-pointed genus 0 curves M_0,n.

The standard basis of the Q-vector space of S_n symmetric divisors on M_0,n is given by the boundary divisors B_i, as we now explain. Let Δ_I be the closure of the locus of curves with two irreducible components meeting at one node such that the marked points with labels in I lie on the first component, and the marked points with labels in I^c lie on the second component. Then B_i= ∑_#I=i Δ_I, and the divisors B₂, ..., B_[n/2] form a basis of the space of symmetric divisors. See [KM].

Symmetric divisors are implemented as hash tables. The key "NumberOfPoints" records the number of marked points, i.e., the n in M_0,n. The keys must be integers between 2 and [n/2]; the value of the key i is the coefficient of B_i when a divisor D is written in the standard basis.

An object of the "SymmetricDivisorM0nbar" class can be created using the function symmetricDivisorM0nbar in either one of two ways: by entering n and a linear polynomial in the B_i’s, or entering n and a list of coefficients.

Methods are included for adding two symmetric divisors, negating a divisor, multiplying a divisor by a scalar, and testing equality of two divisors. The function coefficientList returns the list of the coefficients.

Functions and methods returning an object of class SymmetricDivisorM0nbar :

canonicalDivisorM0nbar -- returns the class of the canonical divisor on the moduli space of stable n-pointed genus 0 curves
kappaDivisorM0nbar -- the class of the divisor kappa
psiDivisorM0nbar -- returns the class of the divisor $\Psi$
scale -- reduces a list or divisor by the gcd of its coefficients
symmetricDivisorM0nbar -- create a symmetric divisor on the moduli space of stable pointed genus 0 curves
symmetrizedConformalBlockDivisor -- computes the symmetrization of the first Chern class of a conformal block vector bundle

Methods that use an object of class SymmetricDivisorM0nbar :

- SymmetricDivisorM0nbar -- negate a symmetric divisor
coefficientList(SymmetricDivisorM0nbar), see coefficientList -- the coefficients of a symmetric divisor D in the standard basis
expression(SymmetricDivisorM0nbar) (missing documentation)
isExtremalSymmetricFDivisor(SymmetricDivisorM0nbar), see isExtremalSymmetricFDivisor -- tests whether an S_n symmetric divisor spans an extremal ray of the cone of symmetric F-divisors
isSymmetricFDivisor(SymmetricDivisorM0nbar), see isSymmetricFDivisor -- checks whether a symmetric divisor intersects all the F-curves nonnegatively
killsCurves(SymmetricDivisorM0nbar), see killsCurves -- given an S_n symmetric divisor D, produces a list of symmetric F-curves C such that C dot D = 0
net(SymmetricDivisorM0nbar) (missing documentation)
Number * SymmetricDivisorM0nbar -- multiply a symmetric divisor by a number
scale(SymmetricDivisorM0nbar), see scale -- reduces a list or divisor by the gcd of its coefficients
symmetricCurveDotDivisorM0nbar(List,SymmetricDivisorM0nbar), see symmetricCurveDotDivisorM0nbar -- the intersection number of a symmetric F-curve C with the symmetric divisor D
SymmetricDivisorM0nbar + SymmetricDivisorM0nbar -- add two $S_n$ symmetric divisors
SymmetricDivisorM0nbar == SymmetricDivisorM0nbar -- test equality of two symmetric divisor classes on $\bar{M}_{0,n}$

For the programmer

The object SymmetricDivisorM0nbar is a type, with ancestor classes HashTable < Thing.