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Machine Learning Summer School on Theory and Practice of Computational Learning

Geometric Inference for Probability Distribution

author: Frederic Chazal, INRIA Sophia Antipolis

Description

Data often comes in the form of a point cloud sampled from an unknown compact subset of Euclidean space. The general goal of geometric inference is then to recover geometric and topological features (Betti numbers, curvatures,...) of this subset from the approximating point cloud data. In recent years, it appeared that the study of distance functions allows to address many of these questions successfully. However, one of the main limitations of this framework is that it does not cope well with outliers nor with background noise. In this talk, we will show how to extend the framework of distance functions to overcome this problem. Replacing compact subsets by measures, we will introduce a notion of distance function to a probability distribution. These functions share many properties with classical distance functions, which makes them suitable for inference purposes. In particular, by considering appropriate level sets of these distance functions, it is possible to associate in a robust way topological and geometric features to a probability measure. If time permits, we will also mention a few other potential applications of this framework.

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Slides
0:00 Geometric Inference for Probability distributions
0:01 Motivation
1:03 Geometric inference
4:21 Distance functions for geometric inference
7:52 Stability properties of the offsets
10:16 The problem of outliers
12:32 The three main ingredients for stability
16:11 Replacing compact sets by measures
17:42 Distance between measures
20:51 Wasserstein distance
23:18 The distance to a measure
24:56 Unstability of µ -> σµ,m
27:13 The distance function to a measure. (1)
29:08 The distance function to a measure. (2)
29:13 The distance function to a measure. (1)
29:16 The distance function to a measure. (2)
30:26 1-Concavity of the squared distance function
30:40 Proposition
30:43 1-Concavity of the squared distance function
30:48 Proposition
31:19 Another expression for dµ,m0 (1)
32:45 Another expression for dµ,m0 (2)
34:36 Theorem
36:18 Consequences of the previous properties
36:30 Example : square with outliers (1)
36:58 Example : square with outliers (2)
37:03 Example : square with outliers (1)
37:07 Example : square with outliers (2)
37:30 A 3D example
38:27 A reconstruction theorem
39:44 k-NN density estimation vs distance to a measure (1)
40:32 k-NN density estimation vs distance to a measure (2)
40:38 k-NN density estimation vs distance to a measure (1)
40:52 k-NN density estimation vs distance to a measure (2)
41:28 k-NN density estimation vs distance to a measure (3)
41:47 k-NN density estimation vs distance to a measure (4)
42:42 Pushing data along the gradient of dµ,m0 (1)
44:22 Pushing data along the gradient of dµ,m0 (2)
45:46 Take-home messages

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