## Time: Thursdays 5:00 - 6:30 PM     Venue: AVW 2168

Fall 2016

 September 8 Prashanth L. A. UMD Model-free optimization of human preferences in stochastic systems Abstract: In several real-world systems involving humans, traditional expected value cannot explain the observed behavior and incorporating distortions in the underlying probabilities of the system can alleviate this problem. Cumulative prospect theory (CPT) is a very popular approach that is based on probabilistic distortions and is more general than the expected value. We bring this idea to a stochastic optimization framework and propose algorithms for both estimation and optimization of the CPT-value objective. We propose an empirical distribution function based scheme to estimate the CPT-value and then use this scheme in the inner loop of a CPT-value optimization procedure. We propose both gradient-based as well as gradient-free CPT-value optimization algorithms, that are based on two well-known simulation optimization ideas: simultaneous perturbation stochastic approximation (SPSA) and model-based parameter search (MPS), respectively. We provide theoretical convergence guarantees for all the proposed algorithms and also illustrate the usefulness of CPT-based criteria in a traffic signal control application. The majority of the talk will be accessible to a broad audience. ** Joint work with Cheng Jie, Michael Fu, Steve Marcus and Csaba Szepesvari. September 15 Alborz Alavian UMD Polynomial Algorithms for Lower-Bounds on the k-th Singular Value of a Polynomial Matrix Abstract: This talk is on the minimization of the k-th singular value of a general polynomial matrix. We will discuss an equivalent optimization problem that is composed of a polynomial objective subjected to polynomial constraints, and a further rank constraint. We will then discuss two methods on the rank constraint to write this problem as a polynomial optimization problem. This can be used in conjunction with Sum-of-Squares (SOS) techniques to derive a lower-bound on the k-th singular value of a polynomial matrix. Time allowing, we will discuss applications of this problem in deriving bounds on how far an LTI dynamic system is from loosing decentralized controllability. September 29 Zitan Chen UMD The Capacity of Online (Causal) q-ary Error-Erasure Channels Abstract: In the q-ary online (causal) channel coding model, a sender wishes to communicate a message to a receiver by transmitting a codeword ${\bf x} =(x_1,...,x_n)$ symbol-by-symbol via a channel limited to at most np errors (symbol changes) and np* erasures. The channel is online'' (i.e., causal") in the sense that at the i-th step of communication the channel decides whether to corrupt the i-th symbol or not only based on its view of the symbols $(x_1,...,x_i)$. This is in contrast to the classical adversarial channel in which the corruption is chosen with full knowledge of the sent codeword ${\bf x}$. The capacities of binary online bit-flip-only channels, and separately binary online erasure-only channels have been characterized recently. In this work we extend prior results in two important ways. First, we obtain the capacity of q-ary online channels for general $q$ (rather than just $q$=2). Second, we analyze combined error-erasure corruption models (rather than studying them separately). Characterization of this much broader class of symmetric online channels gives a fuller understanding of the effects of causality on jamming adversaries. October 6 P. Vijay Kumar IISc and USC Binary Codes with Locality for Multiple Erasures Having Short Block Length Abstract: This paper considers linear, binary codes having locality parameter $r$, that are capable of recovering from $t$ greater than or equal to $2$ erasures and which additionally, possess short block length. The focus is mostly on codes which can recover from multiple erasures in a sequential manner. The case of recovery from multiple erasures in parallel will be discussed, in the restricted setting where the column and row weight of the parity-check matrix are fixed, and where the parity checks on a code symbol are pairwise orthogonal. This is joint work with S. B. Balaji and K. P. Prasanth. October 13 Zitan Chen, continued UMD The Capacity of Online (Causal) q-ary Error-Erasure Channels Abstract: In the q-ary online (causal) channel coding model, a sender wishes to communicate a message to a receiver by transmitting a codeword ${\bf x} =(x_1,...,x_n)$ symbol-by-symbol via a channel limited to at most np errors (symbol changes) and np* erasures. The channel is online'' (i.e., causal") in the sense that at the i-th step of communication the channel decides whether to corrupt the i-th symbol or not only based on its view of the symbols $(x_1,...,x_i)$. This is in contrast to the classical adversarial channel in which the corruption is chosen with full knowledge of the sent codeword ${\bf x}$. The capacities of binary online bit-flip-only channels, and separately binary online erasure-only channels have been characterized recently. In this work we extend prior results in two important ways. First, we obtain the capacity of q-ary online channels for general $q$ (rather than just $q$=2). Second, we analyze combined error-erasure corruption models (rather than studying them separately). Characterization of this much broader class of symmetric online channels gives a fuller understanding of the effects of causality on jamming adversaries. October 20 Vinay Praneeth Boda UMD Sampling Rate Distortion Abstract: In this talk, we consider a discrete memoryless multiple source with $m$ components of which $k \leq m$ possibly different sources are sampled at each time instant and jointly compressed in order to reconstruct all the $m$ sources under a given distortion criterion. A new notion of sampling rate distortion function(SRDf) is introduced, and is characterized first for the case of fixed-set sampling. Next, different forms of randomized sampling in their increasing order of complexity are introduced and their corresponding SRDfs are characterized. For independent random sampling performed without knowledge of the source outputs, it is shown that the SRDf is the same regardless of whether or not the decoder is informed of the sequence of sampled sets. Next, for memoryless random sampling, where the sampling can depend on the source outputs, it is shown that deterministic sampling, characterized by a conditional point-mass, is optimal and suffices to achieve the sampling rate distortion function. This is joint work with Prof. Prakash Narayan. October 27 Yingquan Wu Micron Technology LDPC for flash - from theory to practice Abstract: This talk first presents the challenges of error-correcting coding in flash memories. It then gives the practical overview of LDPC codes. Finally, it reveals some insights of LDPC optimization for flash memories. November 3 Paul Cuff Princeton University TBA Abstract: TBA November 10 Dipankar Maity UMD TBA Abstract: TBA November 17 Ahmed Arafa UMD TBA Abstract: TBA December 8 Himanshu Tyagi IISc TBA Abstract: TBA

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