Canonical foliations of neural networks: application to robustness

Adversarial attack is an emerging threat to the trustability of machine learning. Understanding these attacks is becoming a crucial task. We propose a new vision on neural network robustness using Riemannian geometry and foliation theory, and create a new adversarial attack by taking into account the curvature of the data space. This new adversarial attack called the "dog-leg attack" is a two-step approximation of a geodesic in the data space. The data space is treated as a (pseudo) Riemannian manifold equipped with the pullback of the Fisher Information Metric (FIM) of the neural network. In most cases, this metric is only semi-definite and its kernel becomes a central object to study. A canonical foliation is derived from this kernel. The curvature of the foliation's leaves gives the appropriate correction to get a two-step approximation of the geodesic and hence a new efficient adversarial attack. Our attack is tested on a toy example, a neural network trained to mimic the $\texttt{Xor}$ function, and demonstrates better results that the state of the art attack presented by Zhao et al. (2019).

Classifying histograms of medical data using information geometry of beta distributions

In this paper, we use tools of information geometry to compare, average and classify histograms. Beta distributions are fitted to the histograms and the corresponding Fisher information geometry is used for comparison. We show that this geometry is negatively curved, which guarantees uniqueness of the notion of mean, and makes it suitable to classify histograms through the popular K-means algorithm. We illustrate the use of these geometric tools in supervised and unsupervised classification procedures of two medical data-sets, cardiac shape deformations for the detection of pulmonary hypertension and brain cortical thickness for the diagnosis of Alzheimer's disease.