# June 2019 Prize Spotlight: SIAM Conference on Control and Its Applications

Congratulations to the following members of the SIAM community who received awards at the SIAM Conference on Control and its Applications (CT19), held June 19-21, 2019 in Chengdu, China.

- Miroslav Krstić - W. T. and Idalia Reid Prize
- Hai Dang Nguyen - SIAM Activity Group on Control and Systems Theory Prize
- Daniel Hernández-Hernández and Mihai Sîrbu - SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize
- Nader Motee and Qiyu Sun - SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize

## Miroslav Krstić - W. T. and Idalia Reid Prize

The W. T. and Idalia Reid Prize in Mathematics is awarded annually to an individual for research in or other contributions to the broadly defined areas of differential equations and control theory. The prize may be given for a single notable achievement or for a collection of such achievements. The award recognizes Krstić for outstanding contributions to control and stabilization of nonlinear deterministic and stochastic dynamical systems governed by ordinary differential, functional differential, and partial differential equations. In addition to high-level theoretical work, he has developed applications in engineering, mechanics, and industry.

Miroslav Krstić is a distinguished professor in the Department of Mechanical and Aerospace Engineering and founding director of the Cymer Center for Control Systems and Dynamics (CCSD) at the University of California San Diego (UCSD), where he has been on the faculty since 1997. As a graduate student, he won student best paper awards at both the IEEE Conference on Decision & Control (CDC) and the American Control Conference (ACC). He earned his Ph.D. at the University of California Santa Barbara in 1994, winning the UC Santa Barbara Lancaster Best Dissertation Award. From the American Society of Mechanical Engineers (ASME), he has received the Oldenburger Medal, the Nyquist Lecture Prize, and the Paynter Outstanding Investigator Award. He has also received the Ragazzini Education Award, Chestnut Textbook Prize, and IEEE Control Systems Society Distinguished Member Award. He was the first engineer awarded the UCSD Chancellor’s Associates Award for Excellence in Research in Sciences and Engineering.

Krstić is a foreign member of the Serbian Academy of Sciences and Arts and of the Academy of Engineering of Serbia and has been elected Fellow of seven scientific societies - IEEE, IFAC, ASME, SIAM, AAAS, IET (UK), and AIAA (Assoc. Fellow). He serves as Editor-in-Chief of *Systems & Control Letters*, following fifteen years of Senior Editor service in *Automatica* and *IEEE Transactions on Automatic Control.* Krstić has coauthored thirteen books on adaptive, nonlinear, and stochastic control, extremum seeking, control of PDE systems including turbulent flows, and control of delay systems.

**Q:** *Why are you excited to be awarded the W. T. and Idalia Reid Prize?*

**A:** I am excited to be awarded the Reid Prize - an award to which its prior recipients have brought immense mathematical distinction - because of what it means for the careers of several generations of my students who have trusted my recommendation to tune out the trends and work instead on PDE stabilization.

**Q:** *Could you tell us a bit about the research that won you the prize?*

**A:** I have spent the last twenty years developing explicit control algorithms for stabilization of various PDE systems inspired by physics and engineering. To solve PDE stabilization problems I developed a continuum version of the backstepping method, which I had crafted in the 1990s for nonlinear ODEs with unknown parameters and stochastic disturbances. In addition to parabolic, hyberbolic and other PDE classes, I’ve focused also on coupled PDE systems from different classes and on systems that involve PDEs and ODEs simultaneously, as well as on PDEs whose parameters are unknown and require “adaptive” control laws.

**Q:** *What does your research mean to the public?*

**A:** My work on extremum seeking control of extreme ultraviolet light for photolithography has facilitated a hundredfold increase in the area density in the manufacturing of computer chips. My PDE observers are enabling advances in control of lithium ion batteries and offshore oil drilling.

**Q:** *What does being a SIAM member mean to you?*

**A:** As a theoretical engineer, who does mathematics for the love of it and not because my job mandates it, having a societal association with my field’s most mathematically sophisticated colleagues is the principal satisfaction I derive from my membership in SIAM.

## Hai Dang Nguyen - SIAM Activity Group on Control and Systems Theory Prize

The SIAM Activity Group on Control and Systems Theory awards the SIAM Activity Group on Control and Systems Theory Prize every two years to one individual in their early career for distinguished research contributions to the mathematical theory of systems and control in the three calendar years preceding the award year. One key paper published in English in a peer-reviewed journal must be cited as evidencing the contributions. The candidate must be either a graduate student or the key paper must have been published no more than three years after the candidate received their PhD.

Hai Dang Nguyen is an assistant professor in the Department of Mathematics at the University of Alabama. He received his PhD in applied mathematics from the Department of Mathematics at Wayne State University in 2018. His research interests include stochastic processes, stochastic control, dynamical systems and their applications in ecology and infectious disease.

**Q:** *Why are you excited about winning the prize?*

**A:** It is a great honor for me to receive the SIAM Activity Group on Control and Systems Theory Prize. I am thrilled that my research contributions have been recognized by my distinguished colleagues and SIAM. I am very excited to give the lecture at the 2019 SIAM Conference on Control and its Applications. I am very grateful to the people who nominated me, and my thanks also go to the SIAM Activity Group on Control and Systems the prize selection committee.

**Q:** *Could you tell us a bit about the research that won you the prize?*

**A:** My research focuses on control and systems theory, in particular, stabilization and stability of stochastic differential systems with or without delays and their applications to population dynamics in order to understand how the fluctuations of environments facilitate or suppress the growth of interacting species or infectious disease. Understanding stochastic mechanisms is the key to enacting biological control strategies and conservation policies so as to maintain the abundance of populations and to control epidemics.

**Q:** *What does your research mean to the public?*

**A:** Our research aims to develop technical tools combining control and systems theory and probability theory with applications to ecology and epidemiology to enhance our understanding of how species and diseases evolve under environmental fluctuations, especially as climate change is now a resurgent threat to ecological sustainability. We also hope to develop control-theory-based harvesting strategies that keep the balance between ecological and economic benefits.

**Q:** *What does being a SIAM member mean to you?*

**A:** I have been a member of SIAM and SIAG/CST since I was a graduate student. SIAM activities are a valuable means of communication for mathematicians, scientists, engineers, and practitioners. My research has enormously benefited from SIAM publications, presentations, and discussions during SIAM conferences. They help me to keep posted on contemporary research, to build interdisciplinary collaborations, and to disseminate my ideas.

## Daniel Hernández-Hernández and Mihai Sîrbu - SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize

The SIAM Activity Group on Control and Systems Theory awards SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize to recognize noteworthy papers published in *SIAM Journal on Control and Optimization* (SICON). It is awarded to the author or authors of the two most outstanding papers, as determined by the selection committee, published in SICON in the three calendar years preceding the award year.

Hernández-Hernández and Sîrbu were recognized for their paper, “Zero-Sum Stochastic Differential Games Without the Isaacs Condition: Random Rules of Priority and Intermediate Hamiltonians,” *SIAM Journal on Control and Optimization *(2018), Volume 56, Issue 3. This paper provides a novel and innovative analysis of zero-sum stochastic games which do not satisfy the Isaacs condition, employing the notion of intermediate Hamiltonians. It makes a fundamental contribution to zero sum stochastic games and employs both a novel model and innovative mathematical analysis. It is expected that this work will open new directions in stochastic games and in the study of nonlinear PDEs with ordered Hamiltonians.

Daniel Hernández-Hernández received his PhD in 1993 from the Department of Mathematics of the Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV) in México. Since 1999, he has been a professor in the Department of Probability and Statistics of the Research Center for Mathematics (CIMAT) in Guanajuato. From 2009 – 2014, he was associate editor of *SIAM Journal on Control and Optimization*.

**Q:** *Why are you excited to be awarded this prize?*

**A:** We are excited to receive the SIAG/CST Best SICON Paper Prize for several reasons. *SIAM Journal on Control and Optimization* is one of the longest-established SIAM journals. It has been the main source of information for us about important developments in the theory of control and games and the top choice for publishing our own papers in the area. It is an honor to have our paper recognized among so many interesting contributions.

**Q:** *Could you tell us a bit about the research that won you the prize?*

**A:** In dynamic games, the information available to each player has a fundamental role not only in how strategies are defined, but in the very concept of value. The decisive piece of information is the knowledge of the opponent's action in real time. Briefly, in two-person zero-sum stochastic games in which both players observe the state of the system, there can be three situations: the first player can see the second player's actions in real time, the exact opposite (the second player has knowledge of the first player's actions instantaneously), or neither player has such knowledge. If the Isaacs condition holds, all these three situations lead to the same value. If the Isaacs condition does not hold, then three different (ordered) values are obtained (players randomize their actions if there is no real time information about each other). The game of “rock-paper-scissors” describes a toy example of a one-period deterministic game without Isaacs conditions. Our work shows that any value in between the one for complete informational advantage for the first player or for the second player is the value of a game where the informational advantage is decided dynamically according to a (repeated) coin toss. The two players take random turns on who observes the other's actions in real time.

Q: *What does your research mean to the public?*

A: Imagine a game of "rock-paper-scissors" between player A and player B, where both players stake one dollar. If player A sees first the action of B, then A wins one dollar (for sure). The opposite happens if B sees first what A is doing, in which case A loses one dollar. Taking the point of view of player A, the value of this game is one if A has informational advantage and negative one in the opposite situation. The real life game does not give an advantage to any player. In this case, the equilibrium strategies of the two players is for both of them to independently draw from a box (this does not need to be a physical draw, but a mental exercise) one ticket out of three choices: rock, paper or scissors. This is called randomization and leads to an expected value of zero dollars (for player A). We imagine an alternative game where a coin is tossed and then, depending on the outcome, either A or B has informational advantage. If the coin is fair, the value of this new game is still zero. With a biased coin, we obtain a game with a different expected value (at least negative one and at most one). Our work models and analyzes similar continuous-time dynamic games, where a biased coin is tossed very fast to decide the informational advantage, and the outcome of the game actually contains additional randomness (unlike rock-paper-scissors).

Q: *What does participation in SIAM mean to you?*

A: SIAM publishes some of the most important and influential journals in applied mathematics and organizes distinguished conferences and workshops. Having access to these and to the very extensive network of researchers represents for us a real professional opportunity. SIAM has played a crucial role in advancing our academic goals.

## Nader Motee and Qiyu Sun - SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize

The SIAM Activity Group on Control and Systems Theory awards the SIAM Activity Group on Control and Systems Theory Best SICON Paper Prize to recognize noteworthy papers published in *SIAM Journal on Control and Optimization* (SICON). It is awarded to the author or authors of the two most outstanding papers, as determined by the selection committee, published in SICON in the three calendar years preceding the award year.

Motee and Sun were recognized for their paper, “Sparsity and Spatial Localization Measures for Spatially Distributed Systems,” *SIAM Journal on Control and Optimization *(2017), Volume 55, Issue 1. This paper makes a fundamental contribution to spatially distributed systems theory, showing in particular that quadratically optimal state feedback controllers for spatially decaying systems are sparse and spatially localized.

Nader Motee is an associate professor in the Department of Mechanical Engineering and Mechanics at Lehigh University in Pennsylvania. He received his BSc from Sharif University of Technology, Tehran, Iran, in 2000 and his PhD from the University of Pennsylvania in 2007, both degrees in electrical and systems engineering. He was a postdoctoral scholar in the Control and Dynamical Systems Department at California Institute of Technology. Motee is a recipient of the 2008 American Automatic Control Council (AACC) O. Hugo Schuck Best Paper Award, NSF CAREER and Young Investigator Program awards from AFOSR and ONR. His current research areas include networked control systems, robot learning and perception.

**Q:** *Why are you excited to be awarded the SIAG/CST Best SICON Paper Prize?*

** **

**A:** This award is a timely recognition of a rapidly growing research area on issues related to sparsity and localization of sensing, estimation, and control mechanisms in spatially distributed systems. We are hopeful that this honor will motivate and attract more young researchers to undertake existing challenges in the area of distributed control systems.

**Q:*** Could you tell us a bit about the research that won you the prize?
*

**A:** Our work is motivated by applications of an important family of spatially distributed systems where coupling between every two subsystems decays as a function of their (spatial) distance. The applications of spatially decaying systems include models of spatially distributed power networks with sparse interconnection topologies, multi-agent systems with nearest-neighbor coupling structures, arrays of micro-mirrors and micro-cantilevers, and spatially discretized partial differential equation (PDE) models of systems arising in fluid flow control. In this work, our focus is on spatially decaying linear systems where the state-space matrices have some off-diagonal decay structure. The goal is to establish a relationship between spatial decay properties of spatially decaying systems, on the one hand, and sparsity and spatial localization properties of their optimal feedback controllers, on the other hand. The main challenge is to bridge the two fundamental features: spatial decay and sparsity. We address this challenge by developing a functional calculus and establish inverse preservation for a family of matrix algebras to approximate sparse matrices and to measure localization and sparsity of state-space matrices. Our result has the broad implication that the optimal solution of several well-known filtering and robust control design methods, such as LQR, LQG, H_{2}, and H∞, will have the spatial decay property; namely, for a linear system with off-diagonally decaying state-space matrices, their optimal observer and state feedback control gains will be spatially localized and can be efficiently approximated by sparse matrices.

**Q:*** What does your research mean to the public?*

** **

**A:** Our results suggest that optimal solutions to estimation and control design problems for a broad class of systems inherit spatial decay and localization properties from their underlying dynamics. To make this clear, let us consider a large-scale platoon of self-driving vehicles, where two vehicles are coupled if they can exchange information using their onboard communication modules. In practice, these modules have finite signal range. Our theoretical findings predict that these vehicles may only communicate with their near-by neighbors and efficiently implement their estimation and control algorithms in a localized and distributed fashion. This significantly reduces communication requirements in a large-scale platoon. Our results have a broader impact on many other applied mathematics and engineering problems where problem formulation enjoys some specific spatially decaying properties. Two fields that have great potentials to be impacted by our results are problems related to sensing, estimation, and control of systems governed by partial differential equations and nonlinear spatially decaying systems as well as partitioning and localizing large-scale optimization problems that arise in robotics and transportation networks.

**Q: ***What does participation in SIAM mean to you?*

**A:** The SIAM journals, especially SICON, not only have held high standards in accepting and publishing papers, but also have been a great source of motivation for engineers and mathematicians to collaborate on practically relevant research problems. We are very honored to be part of his active community.