/tags/2015-fall/index.xml 2015 Fall - McGill Statistics Seminars
  • A unified algorithm for fitting penalized models with high-dimensional data

    Date: 2015-09-18

    Time: 15:30-16:30

    Location: BURN 1205

    Abstract:

    In the light of high-dimensional problems, research on the penalized model has received much interest. Correspondingly, several algorithms have been developed for solving penalized high-dimensional models. I will describe fast and efficient unified algorithms for computing the solution path for a collection of penalized models. In particular, we will look at an algorithm for solving L1-penalized learning problems and an algorithm for solving group-lasso learning problems. These algorithm take advantage of a majorization-minimization trick to make each update simple and efficient. The algorithms also enjoy a proven convergence property. To demonstrate the generality of these algorithms, I extend them to a class of elastic net penalized large margin classification methods and to elastic net penalized Cox proportional hazards models. These algorithms have been implemented in three R packages gglasso, gcdnet and fastcox, which are publicly available from the Comprehensive R Archive Network (CRAN) at http://cran.r-project.org/web/packages. On simulated and real data, our algorithms consistently outperform the existing software in speed for computing penalized models and often delivers better quality solutions.

  • Bias correction in multivariate extremes

    Date: 2015-09-11

    Time: 15:30-16:30

    Location: BURN 1205

    Abstract:

    The estimation of the extremal dependence structure of a multivariate extreme-value distribution is spoiled by the impact of the bias, which increases with the number of observations used for the estimation. Already known in the univariate setting, the bias correction procedure is studied in this talk under the multivariate framework. New families of estimators of the stable tail dependence function are obtained. They are asymptotically unbiased versions of the empirical estimator introduced by Huang (1992). Given that the new estimators have a regular behavior with respect to the number of observations, it is possible to deduce aggregated versions so that the choice of threshold is substantially simplified. An extensive simulation study is provided as well as an application on real data.