Now, we’re going to talk a bit about the geometry of the periods, which were completely analytic in nature. As we mentioned, for a compact Riemann surface , we have a period matrix that encodes the complex integration theory on the surface.

### Curves

November 19, 2012

## Understanding Integration III: Jacobians

Posted by Charles Siegel under Abelian Varieties, AG From the Beginning, Algebraic Geometry, Complex Analysis, CurvesLeave a Comment

October 15, 2012

## Understanding Integration II: 1-Forms and Periods

Posted by Charles Siegel under AG From the Beginning, Algebraic Geometry, Complex Analysis, CurvesLeave a Comment

Last time, we discussed integration theory of functions along paths on Riemann surfaces, and then we decided that we wanted to talk about compact Riemann surfaces. Unfortunately, there aren’t any holomorphic functions on them, and meromorphic functions are the wrong choice about what to integrate along curves. Today, we’ll talk about the correct things to integrate, and some of their properties.

October 1, 2012

## Understanding Integration I: Riemann Surfaces

Posted by Charles Siegel under Abelian Varieties, AG From the Beginning, Algebraic Geometry, Complex Analysis, Curves[5] Comments

I’m back! And now, posting from Kavli IPMU in Japan. Now, I’m going to start a series on theta functions, Jacobians, Pryms, and abelian varieties more generally, hopefully with some applications, with my goal being at least one post a week, and eventually establishing a regular posting schedule again. But today, we’ll start with basics, something that should be completely understandable to graduate students and advanced undergraduates.

November 19, 2010

## Prym Varieties

Posted by Charles Siegel under Abelian Varieties, AG From the Beginning, Algebraic Geometry, Cohomology, Curves, Examples, Hodge Theory, MaBloWriMoLeave a Comment

Let be an unramified double cover, where is geneus . Then has genus by the Riemann-Hurwitz formula. Now, encodes lots of information about the geometry of , especially with the additional data of the theta divisor. It turns out that for double covers, there’s an abelian variety that contains a lot of this data.

November 9, 2010

## Low Genus Moduli of Curves

Posted by Charles Siegel under AG From the Beginning, Algebraic Geometry, Curves, Examples, MaBloWriMo, Moduli of Curves[3] Comments

Pretty much everything in this post is in Mumford’s “Curves and their Jacobians,” but I do a couple of things slightly differently, and I intend to supply a bit more detail in some places. The goal here is to construct the moduli of curves of genus for small .

November 4, 2010

## A short post on bitangents

Posted by Charles Siegel under AG From the Beginning, Algebraic Geometry, Curves, Enumerative Geometry, Examples, MaBloWriMo1 Comment

Today’s post will be, as the title says, a bit short. It will, more-or-less finish our current discussion of theta characteristics, and then we’ll get back to something else. But we’ll derive a nice case of a classical formula.

November 3, 2010

## Theta Characteristics and Quadrics in Characteristic Two

Posted by Charles Siegel under Abelian Varieties, AG From the Beginning, Algebraic Geometry, Curves, MaBloWriMoLeave a Comment

Last time we defined theta characteristics as square roots of the canonical bundle. Today, we’re going to analyze the notion a bit, and relate them to quadrics in characteristic two.