Colloquia and Seminars
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Academic Calendar at Technion site.
Upcoming Colloquia & Seminars
Refael Cohen, M.Sc. Thesis Seminar
Advisor: Prof. A. Schuster
As the field of deep learning progresses, and models become larger and larger, training deep neural networks has become a demanding task. The task requires a huge amount of compute power, and can still be very time consuming - especially when using just a single GPU. To tackle this problem, distributed deep learning has come into play, with various asynchronous training algorithms. However, most of these algorithms suffer from decreased accuracy as the number of workers increases. We introduce a new method - Single MomEntum Gradient Accumulation ASGD (SMEGA2), which outperforms existing methods in terms of final test accuracy and scales up to as much as 64 asynchronous workers.
Shadi Endrawis, M.Sc. Thesis Seminar
Advisor: Prof. Tamar Aviv
a large batch of real or simulated robot interaction data, using some data collection policy, and then learn from this data to perform various tasks, using offline learning algorithms. Previous work focused on manually designing the data collection policy, and on tasks where suitable policies can easily be designed, such as random picking policies for collecting data about object grasping. For more complex tasks, however, it may be difficult to find a data collection policy that explores the environment effectively, and produces data that is diverse enough for the downstream task.
In this work, we propose that data collection policies should actively explore the environment to collect diverse data. In particular, we develop a simple-yet-effective goal-conditioned reinforcement-learning method that actively focuses data collection on novel observations, thereby collecting a diverse data-set. The method extends and improves upon popular intrinsic motivation based methods for diverse exploration. We evaluate our method on simulated robot manipulation tasks with visual inputs and show that our method leads to more diverse and evenly distributed data, and more importantly, that the data collection which actively tries to reach novel states leads to significant improvements in the downstream learning tasks.
Current geometry methods for creating and manipulating shapes on computers can sometimes be unreliable and fail unpredictably. Such failures make geometry tools hard to use, prevent non-experts from creating geometry on their computers, and limit the use of geometry methods in domains where reliability is critical. We will discuss my recent efforts in proving when existing methods work as intended, my work in making methods more robust to imperfect input, my work in the creation of new reliable tools with mathematical guarantees, and my future efforts towards a reliable geometry pipeline.
When used for computational fabrication, geometry methods can be expensive, finicky, and require a controlled environment. I will show how simple and economical manufacturing techniques can be used for computational fabrication by exploiting the geometric constraints inherent in specific materials and fabrication methods. We will take a look at how I create geometric tools to design for constrained fabrication techniques, and discuss how computational fabrication can be made both economical as well as accessible in difficult environments.
Oded Stein is a postdoc at MIT at the geometric data processing group. He obtained his MSc from ETH Zurich in 2015, and his PhD from Columbia University in 2020.
Oded is interested in geometry, computer graphics, and applied mathematics. He works on smoothness energies, partial differential equations, discretization of geometric quantities, and their applications to computer graphics and digital fabrication.
Omer Rappoport, M.Sc. Thesis Seminar
Tuesday, 25.1.2022, 10:30
Advisor: Prof. Orna Grumberg and Dr. Yakir Vizel
Constrained Horn Clauses (CHCs) is a fragment of First Order Logic (FOL), that has gained a lot of attention in recent years. One of the main reasons for the rising interest in CHCs is the ability to reduce many verification problems to satisfiability of CHCs. For example, program verification can naturally be described as the satisfiability of CHCs modulo a background theory such as linear arithmetic and arrays. To this end, CHC-solvers can be used as the back-end for different verification tools and allow to separate the generation of verification conditions from the decision procedure that decides if the verification conditions are correct or not.
In our work, we present a novel framework, called LazyHorn, that is aimed at solving the satisfiability problem of CHCs modulo a background theory. The framework is driven by the idea that a set of CHCs can be solved in parts, making it an easier problem for the CHC-solver. Furthermore, solving a set of CHCs can benefit from an interpretation revealed by the solver for its subsets. LazyHorn is lazy in that it gradually extends the set of checked CHCs, as needed. It is also incremental in its use of a CHC solver, supplying it with an interpretation, obtained for previously checked subsets. We have implemented an efficient instance of the framework that is restricted to a fragment of CHCs called linear CHCs.
Tuesday, 25.1.2022, 11:30
Zoom Lecture: https://technion.zoom.us/my/chaimbaskin
Leveragingthe characteristics of convolutional layers, neural networks are extremelyeffective for pattern recognition tasks. However in some cases,their decisions are based on unintended information leading to high performanceon standard benchmarks but also to a lack of generalization to challengingtesting conditions and unintuitive failures. Recentworkhas termed this “shortcut learning” and addressed its presence in multipledomains. In text recognition, we reveal another such shortcut, whereby recognizersoverly depend on local image statistics. Motivated by this, we suggest anapproach to regulate the reliance on local statisticsthat improves text recognition performance.
Ourmethod, termed TextAdaIN, creates local distortions in the feature map whichprevent the network from overfitting to localstatistics. It does so by viewing each feature map as a sequence of elementsand deliberately mismatching fine-grained feature statistics between elementsin a mini-batch. Despite TextAdaIN’s simplicity, extensive experiments show its effectiveness compared to other, morecomplicated methods. TextAdaIN achieves state-of-the-art results on standardhandwritten text recognition benchmarks. Additionally, it generalizes tomultiple architectures and to the domain of scene text recognition. Furthermore, we demonstrate that integrating TextAdaINimproves robustness towards more challenging testing conditions.
Oren Nurielis an applied computer vision scientist at AWS. He holds an MSc degree inComputer Science from the Tel-Aviv University.
Gal Shalom, M.Sc. Thesis Seminar
Wednesday, 26.1.2022, 10:30
Advisor: Prof. Irad Yavneh and Dr. Eran Treister
We propose a novel quasi-Newton method for solving the sparse inverse covariance estimation problem also known as the graphical least absolute shrinkage and selection operator (GLASSO).
This problem is often solved using a second order quadratic approximation. However, in such algorithms the Hessian term is complex and computationally expensive to handle. To this end,our algorithm uses the inverse of the Hessian as a preconditioner to simplify and approximate the quadratic element at the cost of a more complex l1 element. The variables of the resulting preconditioned problem are coupled only by the l1 sub-derivative of each other, which can be guessed with minimal cost using the gradient itself, allowing the algorithm to be parallelized and implemented efficiently on GPU hardware accelerators. Numerical results on synthetic and real data demonstrate that our method is competitive with other state-of-the-art approaches.
Alon Rashelbach (EE, Technion)
Range matching (RM) is a crucial component in computer systems, widely used in address translation, hard drives, network switches, and many more applications. RM is performed whenever one wishes to locate a range that contains an input number, given a large set of ranges. Any page-based mechanism uses RM, as pages are basically ranges. Longest prefix matching (LPM) uses ternary rules, which are also ranges. Firewalls are one example of multidimensional RM since ACL rules consist of several wildcarded fields that can be represented as ranges. Existing algorithms for RM are either page-based, tree-based, or hash-table-based. Either way, they all rely on pointer-chasing techniques, which impede their scalability to large range sets that spill out of the CPU core cache. Furthermore, their inherent lack of access locality and the data-dependent nature of their memory accesses make hardware prefetchers ineffective.
Our research focuses on a new data structure, the Range Query Recursive Model Index (RQ-RMI). RQ-RMI uses shallow neural-nets (NN) for learning the distribution of a given set of ranges, turning the costly lookup operations into NN inference. Crucially, the RQ-RMI training algorithm guarantees a tight bound on its lookup latency, ensures its correctness, and converges fast: it can index 500K ranges in a few hundred milliseconds on a single CPU core.
We develop NuevoMatch (NM), an algorithm for multi-field packet classification, and integrate it into the critical path of the popular, open-source, virtual switch Open vSwitch (OVS). NM scales OVS to support 500K OpenFlow rules with a 12.3X geomean throughput speedup and up to 50K updates per second.
Roei Kisous, M.Sc. Thesis Seminar
Deduplication is a leading method for reducing physical storage capacity when duplicate data is present. This method can be applied on chunks, files, containers, and more. Instead of storing the same physical data multiple times, a pointer is created from each logical copy to the same physical copy, saving the space of the duplicate data. Due to this, data is shared between objects, such as files or entire directories, which result in garbage collection overhead and migration challenges.
In our work, we addressed the general migration problem where files are remapped between different volumes due to system expansion or maintenance. The question of which files and blocks to migrate has been extensively studied in systems without deduplication. However, only simplified migration problems have been considered in the context of deduplicated storage. As part of a migration plan, we aim to minimize the system's size while simultaneously ensuring that the storage load is evenly distributed across the volumes and that the network traffic required for the migration does not exceed its allocation.
Following that, we outline a way to develop effective migration plans using hierarchical clustering. Clustering refers to grouping objects based on their similarity. Hierarchical clustering, in particular, takes the distance between those objects into account. Each object is initially clustered separately, and the process of iterative clustering merges, in each step, two clusters with a minimal distance between them. We are interested in clustering files with high similarity together in order to reduce the amount of physical data while still maintaining low network traffic and a balanced system. Based on each cluster, we calculate data savings, traffic consumed, and load balance achieved and determine the plan's quality.
We show that this method has different tradeoffs between computation time and migration efficiency compared to other algorithms such as greedy and ILP (Integer Linear Programming). Our algorithm achieves almost identical results (and sometimes even better) than ILP, which, theoretically, is optimal, but in much less time.
Ariel Kolikant, M.Sc. Thesis Seminar
Deduplication reduces the size of the data stored in large-scale storage systems by replacing duplicate data blocks with references to their unique copies. This creates dependencies between files that contain similar content and complicates the management of data in the system. In the work presented in this seminar, we have addressed the problem of data migration, where files are remapped between different volumes because of system expansion or maintenance. The challenge of determining which files and blocks to migrate has been studied extensively for systems without deduplication. In the context of deduplicated storage, however, only simplified migration scenarios were considered. In our work we have formulated the general migration problem for deduplicated systems as an optimization problem whose objective is to minimize the system’s size while ensuring that the storage load is evenly distributed between the system’s volumes, and that the network traffic required for the migration does not exceed its allocation. We then modeled an ILP algorithm to solve the migration problem generated, and compared it’s results to two other algorithms solving the same generated migration problem: the greedy algorithm and the clustering algorithm. Our ILP algorithm manages to consistently obtain the best solutions to the problem though it requires significantly larger execution times.