Minimalist Instructions
Refer to arXiv.org:0905.2229 or
here
for mathematical details.
The program does two kinds of calculations: in the tautological module,
on a fixed Hilbert scheme
X[m]B,
as in § 2 of the paper;
and calculations of Chern numbers of tautological bundles,
as in § 3 of the paper.
At present, the program is rather slow in degrees 5 and higher. A faster
version is under construction.
Throughout, we will fix a good pencil X/B
and a line bundle L,
and use the notations:
ω = ωX/B,
g = fibre genus,
d = fibre degree of L,
δ = number of singular fibres,
assumed 1-nodal.
Tautological module calculations
Data is as follows:
•
A monoblock diagonal
Γ(n)[ωa
Lb],
n ≥ 1,
in X[m]B
is represented
by a 1-column matrix written as
M(n,a,b).
A general polyblock diagonal, which can be written as
Γ(n)
[ωaLb]
★Γ(n')
[ωa'Lb']
★...
is represented as
M(n,a,b;n',a',b';...).
Trailing zeros in a column may be omitted.
An analogous class on a single curve of genus x may be
specified as
M(dim_b=0;genus=x;a,b,c;...).
x can be a symbol or a number.
If x is the letter g, it may be omitted.
The weight of M is by definition
dim_b plus the sum of the first row.
dim_b is by default equal to 1, unless specified to be 0 as above.
• A node scroll F
m,n
j;n',n''...
[ωb
Lc,...]
is represented as
F^n_j(n',b,c;...).
The matrix may be empty, written as F^n_j(),
which corresponds to a node scroll over a point.
It always has dim_b=0 and its weight is the weight of the matrix
plus n.
By default, the genus of this object is taken as g-1
but may be reset by inserting genus=x; at the head of the matrix.
For those node scrolls that arise in the calculation with general fibre
genus x,
the program itself will set the genus as x-1.
• A node section
Γ(m)
Fm,n
j;n',n''...
[ωbLc,...]
is represented as
GF^n_j(n',b,c;...).
Its weight is again the weight of the matrix plus n.
The operation of Γ(m)
on these classes is represented by G.
It is unnecessary to specify m because it is determined as
the weight of the argument.
A power of G, input
as G^k, may be applied to any of the above classes,
resulting in a linear combination of such classes.
The degree of zero-dimensional class can be obtained in terms of
ω2, δ etc. using
the operator trivialize.
Chern number calculations
These calculations take place in
Wm(X/B).
To compute ci
(Λm(L))k/m!,
one enters cc(c(m,i)^k).
When the latter is zero-dimensional,
its degree, i.e.
∫Wm(X/B)
ci
(Λm(L))
k/m!
=
∫X[m]B
ci
(Λm(L))k
is evaluated by cc(c(m,i)^k). The Thom-Porteous polynomial
Δ 1(m)(c(m,•))
is evaluated by cc(Delta^m_1).
Examples
(g+d)^10
trivialize(G-L)^4M(1;1;1)
cc(c(3,1)^4)
cc(G_2^2G_3L_3)
cc(c(3,1)^4-3c(3,1)^2c(3,2)+2c(3,1)c(3,3)+c(3,2)2)
cc(Delta^4_1)
sum_(i=0)^1(TiGTFn_(j+1)(dim_b=x;genus=y2;1,i))