Vorträge

Metrics Matter, Examples from Binary and Multilabel Classification

IS Colloquium
  • 21 August 2017 • 11:15 12:15
  • Sanmi Koyejo
  • Empirical Inference meeting room (MPI-IS building, 4th floor)

Performance metrics are a key component of machine learning systems, and are ideally constructed to reflect real world tradeoffs. In contrast, much of the literature simply focuses on algorithms for maximizing accuracy. With the increasing integration of machine learning into real systems, it is clear that accuracy is an insufficient measure of performance for many problems of interest. Unfortunately, unlike accuracy, many real world performance metrics are non-decomposable i.e. cannot be computed as a sum of losses for each instance. Thus, known algorithms and associated analysis are not trivially extended, and direct approaches require expensive combinatorial optimization. I will outline recent results characterizing population optimal classifiers for large families of binary and multilabel classification metrics, including such nonlinear metrics as F-measure and Jaccard measure. Perhaps surprisingly, the prediction which maximizes the utility for a range of such metrics takes a simple form. This results in simple and scalable procedures for optimizing complex metrics in practice. I will also outline how the same analysis gives optimal procedures for selecting point estimates from complex posterior distributions for structured objects such as graphs. Joint work with Nagarajan Natarajan, Bowei Yan, Kai Zhong, Pradeep Ravikumar and Inderjit Dhillon.

Organizers: Mijung Park


Physical Blendshapes - Controllable Physics for Human Faces

Talk
  • 23 August 2017 • 11:00 12:00
  • Yeara Kozlov
  • Aquarium

Creating convincing human facial animation is challenging. Face animation is often hand-crafted by artists separately from body motion. Alternatively, if the face animation is derived from motion capture, it is typically performed while the actor is relatively still. Recombining the isolated face animation with body motion is non-trivial and often results in uncanny results if the body dynamics are not properly reflected on the face (e.g. cheeks wiggling when running). In this talk, I will discuss the challenges of human soft tissue simulation and control. I will then present our method for adding physical effects to facial blendshape animation. Unlike previous methods that try to add physics to face rigs, our method can combine facial animation and rigid body motion consistently while preserving the original animation as closely as possible. Our novel simulation framework uses the original animation as per-frame rest-poses without adding spurious forces. We also propose the concept of blendmaterials to give artists an intuitive means to control the changing material properties due to muscle activation.

Organizers: Timo Bolkart


Dominik Bach - TBA

IS Colloquium
  • 02 October 2017 • 11:15 12:15
  • Dominik Bach

Challenges of writing and maintaining programs for robots

Talk
  • 04 August 2017 • 11:30 12:45
  • Mirko Bordignon
  • AMD meeting

Writing and maintaining programs for robots poses some interesting challenges. It is hard to generalize them, as their targets are more than computing platforms. It can be deceptive to see them as input to output mappings, as interesting environments result in unpredictable inputs, and mixing reactive and deliberative behavior make intended outputs hard to define. Given the wide and fragmented landscape of components, from hardware to software, and the parties involved in providing and using them, integration is also a non-trivial aspect. The talk will illustrate the work ongoing at Fraunhofer IPA to tackle these challenges, how Open Source is its common trait, and how this translates into the industrial field thanks to the ROS-Industrial initiative.

Organizers: Vincent Berenz


Low-dimensional Data Embedding via Robust Ranking

Talk
  • 25 July 2017 • 4:30 5:30
  • Manfred K. Warmuth
  • Seminar room N4.022, department Schölkopf (4th floor)

Organizers: Bernhard Schölkopf


  • Ioannis Papantonis
  • S2 Seminar Room

We present a way to set the step size of Stochastic Gradient Descent, as the solution of a distance minimization problem. The obtained result has an intuitive interpretation and resembles the update rules of well known optimization algorithms. Also, asymptotic results to its relation to the optimal learning rate of Gradient Descent are discussed. In addition, we talk about two different estimators, with applications in Variational inference problems, and present approximate results about their variance. Finally, we combine all of the above, to present an optimization algorithm that can be used on both mini-batch optimization and Variational problems.

Organizers: Philipp Hennig


  • Azzurra Ruggeri

How do young children learn so much about the world, and so efficiently? This talk presents the recent studies investigating theoretically and empirically how children actively seek information in their physical and social environments as evidence to test and dynamically revise their hypotheses and theories over time. In particular, it will focus on how children adapt their active learning strategies. such as question-asking and explorative behavior, in response to the task characteristics, to the statistical structure of the hypothesis space, and to the feedback received. Such adaptiveness and flexibility is crucial to achieve efficiency in situations of uncertainty, when testing alternative hypotheses, making decisions, drawing causal inferences and solving categorization tasks.

Organizers: Philipp Hennig Georg Martius


Machines that learn to see and move

Talk
  • 12 July 2017 • 17:00 18:00
  • Prof. Andrew Blake
  • MPI-IS, ground floor seminar room, N0.002

Neural networks have taken the world of computing in general and AI in particular by storm. But in the future, AI will need to revisit generative models. There are several reasons for this – system robustness, precision, transparency, and the high cost of labelling data. This is particularly true of perceptual AI, as needed for autonomous vehicles, where also the need for simulators and the need to confront novel situations, also will demand generative, probabilistic models.

Organizers: Bernhard Schölkopf Michael Black Stefan Schaal


Deep Learning for stereo matching and related tasks

Talk
  • 12 July 2017 • 11:00 12:00
  • Matteo Poggi
  • PS Seminar Room (N3.022)

Recently, deep learning proved to be successful also on low level vision tasks such as stereo matching. Another recent trend in this latter field is represented by confidence measures, with increasing effectiveness when coupled with random forest classifiers or CNNs. Despite their excellent accuracy in outliers detection, few other applications rely on them. In the first part of the talk, we'll take a look at the latest proposal in terms of confidence measures for stereo matching, as well as at some novel methodologies exploiting these very accurate cues. In the second part, we'll talk about GC-net, a deep network currently representing the state-of-the-art on the KITTI datasets, and its extension to motion stereo processing.

Organizers: Yiyi Liao


Soft bioelectronics: Materials and Technology

Talk
  • 11 July 2017 • 14:00 15:20
  • Prof. Stéphanie Lacour
  • Lecture hall on the ground floor, N0.002 (broadcasted from Stuttgart)

Bioelectronics integrates principles of electrical engineering and materials science to biology, medicine and ultimately health. Soft bioelectronics focus on designing and manufacturing electronic devices with mechanical properties close to those of the host biological tissue so that long-term reliability and minimal perturbation are induced in vivo and/or truly wearable systems become possible. We illustrate the potential of this soft technology with examples ranging from prosthetic tactile skins to soft multimodal neural implants.

Organizers: Diana Rebmann


  • Chris Bauch
  • AGBS seminar room (N4)

Vaccine refusal can lead to outbreaks of previously eradicated diseases and is an increasing problem worldwide. Vaccinating decisions exemplify a complex, coupled system where vaccinating behavior and disease dynamics influence one another. Complex systems often exhibit characteristic dynamics near a tipping point to a new dynamical regime. For instance, critical slowing down -- the tendency for a system to start `wobbling'-- can increase close to a tipping point. We used a linear support vector machine to classify the sentiment of geo-located United States and California tweets concerning measles vaccination from 2011 to 2016. We also extracted data on internet searches on measles from Google Trends. We found evidence for critical slowing down in both datasets in the years before and after the 2014-15 Disneyland, California measles outbreak, suggesting that the population approached a tipping point corresponding to widespread vaccine refusal, but then receded from the tipping point in the face of the outbreak. A differential equation model of coupled behaviour-disease dynamics is shown to illustrate the same patterns. We conclude that studying critical phenomena in online social media data can help us develop analytical tools based on dynamical systems theory to identify populations at heightened risk of widespread vaccine refusal.

Organizers: Diana Rebmann


  • Prof. Peer Fischer
  • MPI-IS, ground floor seminar room, room no. N0.002

This talk will look at hardware-based means of assembling, controlling and driving systems at the smallest of scales, including those that can become autonomous. I will show that insights from physics, chemistry and material engineering can be used to permit the simplification and miniaturization of otherwise bulky systems and that this can give rise to new technologies. One of the technologies we have invented may also permit the development of new imaging devices.

Organizers: Jane Walters Julia Braun


Multi-task Learning with Labeled and Unlabeled Tasks

Talk
  • 05 July 2017 • 14:30 15:45
  • Anastasia Pentina
  • N2 Seminar Room (changed location)

In multi-task learning, a learner is given a collection of prediction tasks and needs to solve all of them. In contrast to previous work, that required that annotated training data must be available for all tasks, I will talk about a new setting, in which for some tasks, potentially most of them, only unlabeled training data is available. Consequently, to solve all tasks, information must be transfered between tasks with labels and tasks without labels. Focussing on an instance-based transfer method I will consider two variants of this setting: when the set of labeled tasks is fixed, and when it can be actively selected by the learner. I will discuss a generalization bound that covers both scenarios and an algorithm, that follows from it, for making the choice of labeled tasks (in the active case) and for transferring information between the tasks in a principled way. I will also show results of some experiments that illustrate the effectiveness of the algorithm.

Organizers: Georg Martius