Upcoming seminars

Upcoming Seminars
(in 7 days)
Seminar: Algebra
On the signature of a quadratic form
Jeremy Jacobson, Emory
Contact: David Zureick-Brown, dzb@mathcs.emoy.edu
Venue: Mathematics and Science Center, Room W306
The signature of a quadratic form plays an important role in the study of quadratic forms in a Witt group. For any algebraic variety X over the real numbers R, it allows one to relate quadratic forms over X to the singular cohomology of the real points X(R). This has applications to bounding the order of torsion in the Witt group of quadratic forms over X.
(in 10 days)
Seminar: Numerical Analysis and Scientific Computing
Approximating Stability Radii
Manuela Manetta, School of Mathematics Georgia Institute of Technology
Contact: Michele Benzi, benzi@mathcs.emory.edu
Venue: Mathematics and Science Center, Room W301
The distance of a n × n stable matrix to the set of unstable matrices, the so-called distance to instability, is a well-known measure of linear dynamical system stability. Existing techniques compute this quantity accurately but the cost is of the order of multiple SVDs of order n, which makes the method suitable for medium-size problems. A new approach is presented, based on Newton’s iteration applied to the pseudospectral abscissa, whose implementation is obtained by discretization of differential equations for low-rank matrices, and is particularly suited for large sparse matrices.