Math 6670, Fall 2017
Allen Knutson
Tues/Thurs 11:40-12:55
Algebra is the offer made by the devil to the mathematician. The devil
says: I will give you this powerful machine, it will answer any
question you like. All you need to do is give me your soul: give up
geometry and you will have this marvelous machine.
—Sir Michael Atiyah, 2002
The book we'll use for reference is at the bottom
here.
Now that we're getting into scheme theory, we'll use
Eisenbud and Harris'
The Geometry of Schemes.
Topics:
Initial notes here.
Next notes.
If you're getting a grade in this class, turn in HW. Due 8/31:
Ex 1.1, 1.2 from those notes
HW due 9/7:
Give the analogue of Taylor's theorem when expanding a
function NN->ZZ as f(d) = \sum_n c_n (d+n choose n).
In particular, show that a polynomial f is integer-valued iff
these c_n are all integer.
What does your analogue give for the non-polynomial function f(d)=2^d?
Prove the Hilbert syzygy theorem for the case of monomial ideals
in x,y.
Let I = < xy-z > and J = < z-t > be ideals in C[x,y,z], where t is
a number. What's the prime decomposition of I+J?
Let I be a homogeneous radical ideal, the intersection of some
minimal prime ideals {P}. Find a formula for the degree of I
(the leading coefficient of the Hilbert polynomial) in terms of
the {P}.
HW due 9/21. Personally, I find the easiest
way to use Macaulay2 to be on my machine from within emacs, but
it is possible to
use it online.
HW due 9/28
HW due 10/5
HW due 10/26 (or the following Tuesday, for undergrads who'd rather
be studying for the GRE):
exercises I-9, 10, 15, 17, 20 from Eisenbud and Harris.
HW due 11/9:
1. Let X be a scheme and R = Gamma(X; O_X) the global functions.
Show in excruciating detail that there is a map of schemes from
X to Spec R.
2. Let R be a commutative O_X-algebra, i.e. a sheaf of algebras
over X with a compatible O_X-module structure. Show in detail
how to define the scheme Spec R in terms of the Specs of the stalks,
and its map to X.
In particular if R = O_X you'd better get the identity X -> X.
3. Exercise I-43 of [EH]
4. Exercise I-46 of [EH]
5a. Compute the fibers of Spec of the map RR[y] -> RR[x,y] / < y-x^2 >
over the points < y-r > for r in RR (here RR = the reals).
5b. Compute the fibers of Spec of the map ZZ -> ZZ[x] / < x^2+1 >
over the points < p > for p in Spec ZZ (here ZZ = the integers).