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===Georg Rutishauser===
 
===Georg Rutishauser===

Revision as of 14:04, 16 November 2020

What is Deep Learning?

Nowadays, machine learning systems are the go-to choice when the cost of analytically deriving closed-form expressions to solve a given problem is prohibitive (e.g., it is very time-consuming, or the knowledge about the problem is insufficient). Machine learning systems can be particularly effective when the amount of data is large, since the statistics are expected to get more and more stable as the amount of data increases. Amongst machine learning systems, deep neural networks (DNNs) have established a reputation for their effectiveness and simplicity. To understand this success as compared to that of other machine learning systems, it is important to consider not only the accuracy performance of DNNs, but also their computational properties. The training algorithm (an iterative application of backpropagation and stochastic gradient descent) is linear in the data set size, making it more appealing in big data contexts than, for instance, support vector machines (SVMs). DNNs do not use branching instructions, making them predictable programs and allowing to design efficient access patterns for the memory hierarchies of the computing devices (exploiting spatial and temporal locality). DNNs are parallelizable, both at the neuron level and at the layer level. These predictability and parallelizability properties make DNNs an ideal fit for modern SIMD architectures and distributed computing systems.


The main drawback of these systems is their size: millions or even billions of parameters are a common feature of many top-performing DNNs, and a proportional amount of arithmetic operations must be performed to process each data sample. Hence, to reduce the pressure of DNNs on the underlying computing infrastructure, research in computational deep learning has focussed on two families of optimizations: topological and hardware-oriented. Topological optimizations are concerned with network topologies (AKA network architectures) which are more efficient in terms of accuracy-per-parameter or accuracy-per-MAC (multiply-accumulate operation). As a specific form of topological optimization, pruning strategies aim at maximizing the number of zero-valued operands (parameters and/or activations) in order to 1) take advantage of sparsity (for storing the model) and to 2) minimize the number of effective arithmetic operations (i.e., the operations not involving zero-valued operands, which must be actually executed). Hardware-oriented optimizations are instead concerned with replacing time-consuming and energy-hungry operations, such as evaluations of transcendent functions or floating-point MAC operations, with more efficient counterparts, such as piecewise linear activation functions (e.g., the ReLU) and integer MAC operations (as in quantized neural networks, QNNs).


Hardware-oriented neural architecture search (NAS)

The problems of topology selection and pruning can be considered instances of the classical statistics problems of model selection and feature selection, respectively. In the scope of deep learning, model selection is also called neural architecture search (NAS). When designing a DNN topology, you have a large number of degrees of freedom at your disposal: number of layers, number of neurons for each layer, connectivity of each neuron, and so on; moreover, the number of choices for each degree of freedom is huge. These properties imply that the design space for a DNN can grow exponentially, making exhaustive searches prohibitive. Therefore, to increase the efficiency of the exploration, stochastic optimization tools are the preferred choice: evolutionary algorithms, reinforcement learning, gradient-based techniques or even random graph generation. An interesting feature of model selection is that specific constraints can be enforced on the search space so that desired properties are always respected. For instance, given a storage budget describing a hard limitation of the chosen computing platform, the network generation algorithm can be limited to propose topologies that do not exceed a given number of parameters. This capability of incorporating HW features as constraints on the search space make NAS algorithms very interesting in the context of generating HW-friendly DNNs.

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Thorir Mar Ingolfsson

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Matteo Spallanzani

Training algorithms for quantized neural networks (QNNs)

The typical training algorithm for DNNs is an iterative application of the backpropagation algorithm (BP) and stochastic gradient descent (SGD). When the quantization is not “aggressive” (i.e., when the parameters and feature maps can be represented as integers with a precision of 8-bits or more), many solutions are available either in specialized literature or in commercial software that can convert models pre-trained with gradient descent to quantized counterparts (post-training quantization). But when the precision is extremely reduced (i.e., 1-bit or 2-bits operands), these solutions can no longer be applied, and quantization-aware training algorithms are needed. The naive application of gradient descent (which in theory is not even correct) to train these QNNs yields major accuracy drops. Hence, it is likely that suitable training algorithms for QNNs require to replace the standard BP+SGD scheme, which is suitable for differentiable optimization, with search strategies that are more apt for discrete optimization.

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Matteo Spallanzani

Hardware Acceleration of DNNs and QNNs

Deep Learning (DL) and Artificial Intelligence (AI) are quickly becoming dominant paradigms for all kinds of analytics, complementing or replacing traditional data science methods. Successful at-scale deployment of these algorithms requires deploying them directly at the data source, i.e. in the IoT end-nodes collecting data. However, due to the extreme constraints of these devices (in terms of power, memory footprint, area cost), performing full DL inference in-situ in low-power end-nodes requires a breakthrough in computational performance and efficiency. It is widely known that the numerical representation typically used when developing DL algorithms (single-precision floating-point) encodes a higher precision than what is actually required to achieve high quality-of-results in inference (Courbariaux et al. 2016); this fact can be exploited in the design of energy-efficient hardware for DL. For example, by using ternary weights, which means all network weights are quantized to {-1,0,1}, we can design the fundamental compute units in hardware without using an HW-expensive multiplication unit. Additionally, it allows us to store the weights much more compact on-chip.

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Gianna Paulin

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Georg Rutishauser

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Moritz Scherer

Prerequisites

We have no strict, general requirements, as they are highly dependent on the exact project steps. The projects will be adapted to the skills and interests of the student(s) -- just come talk to us! If you don't know about GPU programming or CNNs or ... just let us know and we can together determine what is a useful way to go -- after all you are here to learn not only about project work, but also to develop your technical skills.

Only hard requirements:

  • Excitement for deep learning
  • For HW Design projects: VLSI 1, VLSI 2 or equivalent

Tags

All our projects will be categorized into three categories. Therefore, look out for the following tags:

  • Algorithmic - you will mainly make algorithmic evaluations using languages and frameworks like e.g. Python, Pytorch, Tensorflow and our in-house frameworks like Quantlab, DORY, NEMO
  • Embedded Coding - you will implement e.g. c-code for one of our microcontrollers
  • HW Design - you will be designing HW including writing RTL, simulate, synthesize, and layout (backend) some HW


Available Projects

New projects will be uploaded soon. Please visit again in 1-2 weeks or directly contact us.


Projects in Progress


Completed Projects