Fall 2016
September 8  Prashanth L. A. UMD 
Modelfree optimization of human preferences in stochastic systems
Abstract: In several realworld 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 CPTvalue objective. We propose an empirical distribution function based scheme to estimate the CPTvalue and then use this scheme in the inner loop of a CPTvalue optimization procedure. We propose both gradientbased as well as gradientfree CPTvalue optimization algorithms, that are based on two wellknown simulation optimization ideas: simultaneous perturbation stochastic approximation (SPSA) and modelbased parameter search (MPS), respectively. We provide theoretical convergence guarantees for all the proposed algorithms and also illustrate the usefulness of CPTbased 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 LowerBounds on the kth Singular Value of a Polynomial Matrix
Abstract: This talk is on the minimization of the kth 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 SumofSquares (SOS) techniques to derive a lowerbound on the kth 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) qary ErrorErasure Channels
Abstract: In the qary online (causal) channel coding model, a sender wishes to communicate a message to a receiver by transmitting a codeword ${\bf x} =(x_1,...,x_n)$ symbolbysymbol 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 ith step of communication the channel decides whether to corrupt the ith 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 bitfliponly channels, and separately binary online erasureonly channels have been characterized recently.
In this work we extend prior results in two important ways. First, we obtain the capacity of qary online channels for general $q$ (rather than just $q$=2). Second, we analyze combined errorerasure 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 paritycheck 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) qary ErrorErasure Channels
Abstract: In the qary online (causal) channel coding model, a sender wishes to communicate a message to a receiver by transmitting a codeword ${\bf x} =(x_1,...,x_n)$ symbolbysymbol 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 ith step of communication the channel decides whether to corrupt the ith 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 bitfliponly channels, and separately binary online erasureonly channels have been characterized recently.
In this work we extend prior results in two important ways. First, we obtain the capacity of qary online channels for general $q$ (rather than just $q$=2). Second, we analyze combined errorerasure 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 fixedset 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 pointmass, 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 errorcorrecting 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 
Part I: Wiretap Channels with Random States
Part II: Differential Privacy as a Mutual Information Constraint Abstract: In the first part, we propose a new encoding scheme for the wiretap channel setting where a random state is known noncausally to the encoder but not necessarily to the decoder (the GelfandPinsker setting). This setting combines two scenarios with celebrated results in information theorythe wiretap channel and the GelfandPinsker channeland it so happens that essentially the same encoding scheme is optimal for both scenarios individually. A decade ago, Chen and Han Vinck analyzed the secrecy rates achieved by that same encoding scheme. Quite surprisingly, Chia and El Gamal more recently showed that a different encoding scheme which explicitly extracts a key from the state to be used for encryption can sometimes outperform that scheme. In this work, we show a simple superposition code design which performs at least as well as both of these competing schemes, accomplishing the key agreement concept in a more subtle way through the selection of the auxiliary random variables.
In the second part, an information theoretic notion of differential privacy will be presented, which establishes an equivalence between differential privacy and a mutual information constraint. This intuitive definition in terms of mutual information admits very simple proofs of several important properties of differential privacy. 
November 10  Dipankar Maity UMD 
Optimal Strategies for Stochastic Linear Quadratic Differential Games with Costly Information
Abstract: A two player stochastic differential game is considered with a given cost function. The players engage in a noncooperative game where one tries to minimize and the
other tries to maximize the cost. The players are given a dynamical system and their actions serve as the control inputs to the dynamical system. Their goal is to control the state of this dynamical system to optimize the given objective function. We use the term “state of the game” to describe the state of this dynamical system. The challenge is that none of the players have access to the state of the game for all time, rather they can access the state intermittently and only after paying some information cost. Thus the cost structure is nonclassical for a linearquadratic game and it incorporates the value of information. We provide the Nash equilibrium strategy for the players under full state information access at no cost, as well as under costly state information access. The optimal instances for accessing the state information are also explicitly computed for the players.

November 17  Ahmed Arafa UMD 
Optimal Policies for Wireless Networks with Energy Harvesting Transmitters and Receivers: Effects of Decoding Costs
Abstract: We consider the effects of decoding costs in energy harvesting communication systems. In our setting, receivers, in addition to transmitters, rely solely on energy harvested from nature, and need to spend some energy in order to decode their intended packets. We model the decoding energy as an increasing convex function of the rate of the incoming data. In this setting, in addition to the traditional energy causality constraints at the transmitters, we have the decoding causality constraints at the receivers, where energy spent by the receiver for decoding cannot exceed its harvested energy. We first consider the pointtopoint singleuser problem where the goal is to maximize the total throughput by a given deadline subject to both energy and decoding causality constraints. We show that decoding costs at the receiver can be represented as generalized data arrivals at the transmitter, and thereby moving all system constraints to the transmitter side. Then, we consider several multiuser settings. We start with a twohop network where the relay and the destination have decoding costs, and show that separable policies, where the transmitter’s throughput is maximized irrespective of the relay’s transmission energy profile, are optimal. Next, we consider the multiple access channel (MAC) and the broadcast channel (BC) where the transmitters and the receivers harvest energy from nature, and characterize the maximum departure region. In all multiuser settings considered, we decompose our problems into inner and outer problems. We solve the inner problems by exploiting the structure of the particular model, and solve the outer problems by waterfilling algorithms. In this talk, we focus on the singleuser and the BC settings. Time permitting, we will discuss the MAC scenario afterwards.

December 1  Aditya Ramamoorthy Iowa State University 
Combinatorial designs for distributed storage, function computation and coded caching
Abstract: Combinatorial design theory has its roots in recreational mathematics and is concerned with the arrangement of the elements of a finite set into subsets, such that the collection of subsets has certain "nice" properties. In this talk we shall demonstrate that interpreting designs in the right manner yields improved solutions for distributed storage and content caching and novel impossibility results for distributed function computation.
Regenerating codes have been proposed as an efficient mechanism for dealing with the problem of reliability in large scale distributed storage systems. These systems also have additional requirements pertaining to repair. When nodes fail, the system needs to be repaired in a speedy manner by consuming as few resources (number of drives accessed, energy etc.) as possible. We will demonstrate that combinatorial designs allow us to design efficient systems that upon failure can be repaired by simply downloading packets from the surviving nodes. Next, we will show that designs can be used to construct a family of directed acyclic networks that have several interesting properties. In particular, our work shows that the computation rate of such networks depends significantly on the source alphabets. This is in stark contrast with multiple unicast networks where the rate is independent of the source alphabet. We will conclude with an overview of the role of coding in content caching networks and our recent results on how combinatorial designs can play a central role in making coded caching more practical. The talk will be selfcontained; no background in combinatorial designs and/or network coding will be assumed. 
December 8  Himanshu Tyagi/ Shun Watanabe IISc/TUAT 
Interactive Data Exchange
Abstract: An interactive communication protocol for data exchange enables multiple parties observing correlated data to recover each
other's data and attain omniscience. When the data is generated from a known
distribution, a noninteractive communication protocol is known to be
asymptotically rate optimal. In the first part of this talk, we
present an interactive protocol for data exchange for two parties
that can outperform the best noninteractive one for finite data lengths
and is asymptotically optimal even up to the second order
term. We also present a universal variant of this interactive protocol
which does not require the knowledge of the probability distribution of
the data. In the second part of the talk, we present a multiparty universal protocol
for data exchange which performs reasonably well for any given data
sequence (and not only on average for randomly generated data). In our
proposed protocol, the parties communicate in the order of randomness in
their local data and enable data exchange recursively. A key technical
step in the analysis of our protocol is establishing its recursive
nature, namely when a subset of parties recover each other's data, their
rates appear as if this subset of parties were collocated and have been
executing the protocol as a single party.

To
join the mailing list and receive announcements about the talks,
please email praneeth@umd.edu
If you would like to give a talk please send us an email.
Alexander Barg, Prakash Narayan, Vinay Praneeth Boda @umd.edu