1,096 research outputs found
Robustness Verification for Classifier Ensembles
We give a formal verification procedure that decides whether a classifier
ensemble is robust against arbitrary randomized attacks. Such attacks consist
of a set of deterministic attacks and a distribution over this set. The
robustness-checking problem consists of assessing, given a set of classifiers
and a labelled data set, whether there exists a randomized attack that induces
a certain expected loss against all classifiers. We show the NP-hardness of the
problem and provide an upper bound on the number of attacks that is sufficient
to form an optimal randomized attack. These results provide an effective way to
reason about the robustness of a classifier ensemble. We provide SMT and MILP
encodings to compute optimal randomized attacks or prove that there is no
attack inducing a certain expected loss. In the latter case, the classifier
ensemble is provably robust. Our prototype implementation verifies multiple
neural-network ensembles trained for image-classification tasks. The
experimental results using the MILP encoding are promising both in terms of
scalability and the general applicability of our verification procedure
Interactive 3D video editing
We present a generic and versatile framework for interactive editing of 3D video footage. Our framework combines the advantages of conventional 2D video editing with the power of more advanced, depth-enhanced 3D video streams. Our editor takes 3D video as input and writes both 2D or 3D video formats as output. Its underlying core data structure is a novel 4D spatio-temporal representation which we call the video hypervolume. Conceptually, the processing loop comprises three fundamental operators: slicing, selection, and editing. The slicing operator allows users to visualize arbitrary hyperslices from the 4D data set. The selection operator labels subsets of the footage for spatio-temporal editing. This operator includes a 4D graph-cut based algorithm for object selection. The actual editing operators include cut & paste, affine transformations, and compositing with other media, such as images and 2D video. For high-quality rendering, we employ EWA splatting with view-dependent texturing and boundary matting. We demonstrate the applicability of our methods to post-production of 3D vide
Photoelectron spectra of anionic sodium clusters from time-dependent density-functional theory in real-time
We calculate the excitation energies of small neutral sodium clusters in the
framework of time-dependent density-functional theory. In the presented
calculations, we extract these energies from the power spectra of the dipole
and quadrupole signals that result from a real-time and real-space propagation.
For comparison with measured photoelectron spectra, we use the ionic
configurations of the corresponding single-charged anions. Our calculations
clearly improve on earlier results for photoelectron spectra obtained from
static Kohn-Sham eigenvalues
- …