MIT

In addition to the announced topic of Pascal Matrices (abstract below) we will speak briefly about more recent work by Per-Olof Persson on generating simplicial meshes on regions defined by a function that gives the distance from the boundary. Our first goal was a short MATLAB code and we just submitted "A Simple Mesh Generator in MATLAB" to SIAM.

This is joint work with Alan Edelman at MIT and a little bit with Pascal. They had all the ideas.

Put the famous Pascal triangle into a matrix. It could go into a lower triangular L or its transpose L' or a symmetric matrix S:

These binomial numbers come from a recursion, or from the formula for i choose j, or functionally from taking powers of (1 + x).

The amazing thing is that L times L' equals S. (OK for 4 by 4) It follows that S has determinant 1. The matrices have other unexpected properties too, that give beautiful examples in teaching linear algebra. The proof of L L' = S comes 3 ways, I don't know which you will prefer:

1. By induction using the recursion formula for the matrix entries.
2. By an identity for the coefficients i+j choose j in S.
3. By applying both sides to the column vector [ 1 x x² x³ ... ]'.

The third way also gives a proof that S³ = -I but we doubt that result.

The rows of the "hypercube matrix" L² count corners and edges and faces and ... in n dimensional cubes.

An essential first step in many problems of numerical analysis and

computer graphics is to cover a region with a reasonably regular mesh.

We describe a short MATLAB code that begins with a "distance function"

to describe the region: $d(x)$ is the distance to the boundary

(with d

Study the parabolic Hitchin fibrations for Langlands dual groups. Sketch the proof of a duality theorem of the natural symmetries on their cohomology.

Extend the affine Weyl group action in Lecture I to double affine Hecke algebra action, and (hopefully) more examples.

Introduce the parabolic Hitchin fibration, construct the affine Weyl group action on its fiberwise cohomology, and study one example.

This is a special talk outside the normal Computational Mathematics and Application seminar series. Please note it takes place on a Wednesday.

In this lecture, I will illustrate the cobordism hypothesis by presenting some examples. Exact content to be determined, depending on the interests of the audience.