November 30, 2009
Marion Scheepers, Wed. December 2, 2:40-3:30 pm, MG 120.
Online shopping and banking, Wireless communication and remote control devices have become common place. Nontrivial computing power and scanning devices of high power have become readily available. This creates an environment in which information in transit can be easily accessed or changed by unknown parties.
Cryptography is the main tool used to keep information secure. In this talk we will give a brief, motivated, outline of some of the mathematical foundations of cryptography. We also give an example to illustrate that mere possession of a good crypto-system does not guarantee security – one must also use it right.
November 12, 2009
Here are the two parts of the test (part 1, part 2), in case you want a blank copy. As I mentioned, they do not include all topics; they mostly cover material related to chapter 7 of the book, and even then, they are not comprehensive (for example, the second part does not include parts or word problems), but I hope you found them helpful in identifying topics that may require further study or review.
Here are two extra credit problems. Please let me know if you need me to clarify either one.
November 11, 2009
Grady Wright, Wed. November 18, 2:40-3:30 pm, MG 120.
Scattered Node Finite Difference-Type Formulas Generated from Radial Basis Functions with Applications
In the finite difference (FD) method for solving partial differential equations (PDEs), derivatives at a node are approximated by a weighted sum of function values at some surrounding nodes. In the one dimensional case, the weights of the FD formulas are conveniently computed using polynomial interpolation. These one dimensional formulas can be combined to create FD formulas for partial derivatives in two and higher dimensions. This strategy, however, requires that the nodes of the FD “stencils” are situated on some kind of structured grid (or collection of structured grids), which severely limits the application of the FD method to PDEs in irregular geometries. In this talk, we present a novel approach that resolves this problem by allowing the nodes of the FD stencils to be placed freely and by using radial basis function (RBF) interpolation for computing the corresponding weights in the scattered node FD-type formulas. We show how this RBF approach can exactly reproduce all classical FD formulas and how compact FD formulas can be generalized to scattered nodes and RBFs. This latter result is important in that it allows the number of nodes in the stencils to remain relatively low without sacrificing accuracy. For the Poisson equation, these new compact scattered node schemes can also be made diagonally dominant, which ensures both a high degree of robustness and applicability of iterative methods. We conclude the talk with some numerical examples and future applications of the method for geophysical problems.
November 3, 2009
Leming Qu, Wed. November 11, 2:40-3:30 pm, MG 120.
Wavelet Image Restoration and Regularization Parameters Selection
For the restoration of an image based on its noisy distorted observations, we propose wavelet domain restoration by a scale-dependent penalized regularization method (WaveRSL1). The data-adaptive choice of the regularization parameters is based on the Akaike Information Criterion (AIC) and the degrees of freedom (df) are estimated by the number of nonzero elements in the solution. Experiments on some commonly used testing images illustrate that the proposed method possesses good empirical properties.