WNCG - Wireless Networking and Communications Group - Algorithmic Game Theory
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enWNCG Faculty Evdokia Nikolova Co-Organizes Program on Real-Time Decision Making
http://wncg.org/news/wncg-faculty-evdokia-nikolova-co-organizes-program-real-time-decision-making
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"> <p>WNCG faculty member Evdokia Nikolova is co-organizer for a semester-long program on Real-Time Decision Making at UC Berkeley. The program is hosted by the Simons Institute for the Theory of Computing, a collaborative research institute which is a leader in theoretical computer science.</p>
<p>Scientists investigating topics from astrophysics and earth science to urban mobility and energy work with vast amounts of data. The issues they are trying to address have practical outcomes in our day-to-day lives: creation of better earthquake warning methods, observation of astronomical phenomena, improvement of transport infrastructure, and optimization of energy grids, to name a few. One challenge across the board, however, is finding a way to use the data that have been collected in a methodical way that can accurately predict an outcome to a given problem. That’s where theoretical scientists like Professor Nikolova come in.</p>
<p>If the numerical data obtained from real-world scenarios could be translated into a mathematical algorithm, it could mean great advancements for these fields. However, representing real-world situations in a mathematical way isn’t always straightforward.</p>
<p>“In the past five years, I’ve made a deliberate effort to connect to colleagues and researchers from applied disciplines outside of theoretical computer science […] in search [of] interesting algorithmic questions,” Nikolova said, speaking in the program’s kick-off workshop, “Real-Time Decision Making Boot Camp.” Yet in her conversations with these colleagues, she found there was something of a disconnect between the applied scientists and the theoretical scientists like herself.</p>
<p>Scholars in different disciplines often use terminology specific to their field, and they also have distinct ways of visually representing their data. The lack of a mutually understandable way to talk about the issues at the heart of key research questions inevitably limits the chance at successful collaboration.</p>
<p>“I’d think, ‘Well, I don’t really understand what these problems are…in an algorithmic way,’” Nikolova recalled.</p>
<p>The main goal of the Simons Institute’s Real-Time Decision Making program is to bridge that gap—to get participants in all of these disparate fields on the same page from the beginning. Once common ground is established, then a more productive discussion on existing problems and possible modes of solution can take place. The program was designed with the Simons Institute’s larger goal in mind: to “promote fundamental research on the foundations of computer science, as well as to expand the horizons of the field by exploring other scientific disciplines through a computational lens.”</p>
<p>As a co-organizer, Nikolova joins Professors Josh Bloom (UC Berkeley), Steven Low (CalTech), Balaji Prabhakar (Stanford), and program chair Richard Karp (UC Berkeley) in planning the program, which is one of two being hosted at the Simons Institute’s Calvin Lab this semester. Highlights of the program include the aforementioned Boot Camp followed by three weeklong workshops. The Boot Camp session, which took place January 22 through January 26, provided a quick overview of basic concepts in the fields represented by the long-term participants. Nikolova presented a “Brief Introduction to Algorithms, Game Theory and Risk-Averse Decision Making.”</p>
<p>Aside from the workshops, the long-term participants of the program are fully immersed in their research. Since cross-field collaboration is the highlight of the program, they have unstructured days during which they are encouraged to set up meetings with other participants. They also have “tea time” every day—a more casual chance to make connections, catch up on each other’s studies, and foster collaboration naturally.</p>
<p>The program includes almost 50 long-term participants as well as 19 Visiting Graduate Students and Postdocs. Eight Research Fellows round out the list. WNCG student Ali Khodabakhsh, a Graduate Research Assistant in Nikolova’s research group at the University of Texas, is among the attendees, as is WNCG Postdoctoral Fellow Dr. Emmanouil Pountourakis, who won a Simons Fellowship to attend the program.</p>
<p>“<a href="https://simons.berkeley.edu/programs/realtime2018">Real-Time Decision Making</a>” is running at UC Berkeley’s Calvin Lab from January 9 through May 11. Registration for short-term participation in the workshops is free and open to the public. Upcoming workshops in the program include “Applications in the Natural Sciences and Physical Systems,” “Societal Networks,” and “Mathematical and Computational Challenges in Real-Time Decision Making.” For those who can’t make it in person, each workshop will be recorded for live-stream, and video will also be accessible after the event.</p>
</div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-above"><div class="field-label">Keywords: </div><div class="field-items"><div class="field-item even"><a href="/tags/algorithmic-game-theory">Algorithmic Game Theory</a></div><div class="field-item odd"><a href="/tags/data-analytics">Data Analytics</a></div><div class="field-item even"><a href="/tags/simons-institute">Simons Institute</a></div><div class="field-item odd"><a href="/tags/computer-science">computer science</a></div></div></div><div class="field field-name-field-publish-date field-type-datetime field-label-above"><div class="field-label">Publish Date: </div><div class="field-items"><div class="field-item even"><span class="date-display-single">Wednesday, March 7, 2018</span></div></div></div><div class="field field-name-field-more-information field-type-link-field field-label-above"><div class="field-label">More Information: </div><div class="field-items"><div class="field-item even"><a href="https://simons.berkeley.edu/programs/realtime2018" target="_blank" class="more-information">More Information</a></div></div></div><div class="field field-name-field-image field-type-image field-label-above"><div class="field-label">Key Image: </div><div class="field-items"><div class="field-item even"><img src="http://wncg.org/sites/wncg.org/files/Nikolova_Power_Grid.jpg" width="350" height="250" /></div></div></div><div class="field field-name-field-related-faculty field-type-node-reference field-label-above"><div class="field-label">Related Faculty: </div><div class="field-items"><div class="field-item even"><a href="/people/faculty/evdokia-nikolova">Evdokia Nikolova</a></div></div></div><div class="field field-name-field-related-students field-type-node-reference field-label-above"><div class="field-label">Related Researchers: </div><div class="field-items"><div class="field-item even"><a href="/people/students/ali-khodabakhsh">Ali Khodabakhsh</a></div></div></div><div class="field field-name-field-feature field-type-list-boolean field-label-above"><div class="field-label">Feature: </div><div class="field-items"><div class="field-item even">No</div></div></div>Wed, 07 Mar 2018 18:51:11 +0000jlu754134 at http://wncg.orghttp://wncg.org/news/wncg-faculty-evdokia-nikolova-co-organizes-program-real-time-decision-making#commentsTraffic assignment with uncertain travel times
http://wncg.org/research/briefs/traffic-assignment-uncertain-travel-times
<div class="field field-name-field-publish-date field-type-datetime field-label-hidden"><div class="field-items"><div class="field-item even"><span class="date-display-single">Wednesday, March 19, 2014</span></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"> <p>As vehicles become smarter, increasingly automated and with access to massive amounts of data, they become better equipped to commucate, coordinate and compute optimal routes so as to minimize congestion. Such coordination is modeled by routing games, where a central goal is to understand and compute a socially optimal traffic assignment that minimizes overall congestion. </p>
<p>WNCG Prof. Nikolova and Prof. Stier-Moses from Universidad Di Tella, Argentina are laying the theoretical foundation of how risk aversion and uncertainty transform classic routing games. Routing games were one of the principal examples in the development of algorithmic game theory. In these games, multiple users need to route between different source-destination pairs and edges are congestible, namely, each edge delay is a non-decreasing function of the flow or number of users on the edge. A key motivation for studying routing games is understanding and mitigating congestion in transportation networks. However, unlike the classic routing game model where edge delays are known, in reality they are uncertain—heavy and uncertain traffic conditions exacerbate the commuting experience of millions of people across the globe. When planning important trips, commuters typically add an extra buffer to the expected trip duration to ensure on-time arrival.</p>
<p>Motivated by this, in a recent paper Nikolova and Stier-Moses propose and analyze a new traffic assignment model that takes into account uncertain travel times and risk-averse users. Users capture the tradeoff between travel times and their variability in a mean-standard deviation objective, defined as the mean travel time plus a risk-aversion factor times the standard deviation of travel time along a path. The paper provides a characterization of an equilibrium traffic assignment and provides conditions when it exists. The main challenge is posed by the users’ risk aversion, since the mean-standard deviation objective is nonconvex and nonseparable, meaning that a path cannot be split as a sum of edge costs. As a result, even an individual user’s subproblem—a stochastic shortest path problem—is a nonconvex optimization problem for which no polynomial time algorithms are known. In turn, the mathematical structure of the traffic assignment model with stochastic travel times is fundamentally different from the classic deterministic model. In particular, an equilibrium characterization requires exponentially many variables, one for each path in the network, since an edge-flow has multiple possible path-flow decompositions that are not equivalent. Because of this, characterizing the equilibrium and the socially-optimal traffic assignment, which minimizes the total user cost, is more challenging than in the traditional deterministic setting. Nevertheless, the paper proves that both can be encoded by a representation with just polynomially-many paths. Also, under the assumption that the standard deviations of travel times are independent from edge loads, it shows that the worst-case ratio between the total user cost in an equilibrium and that of an optimal solution is not higher than the analogous ratio in the deterministic setting. In other words, uncertainty does not further degrade the system performance in addition to strategic user behavior alone.</p>
<p>Read full journal paper: <a href="http://users.ece.utexas.edu/~nikolova/papers/stochWardropEqFinalOR.pdf" target="_blank">http://users.ece.utexas.edu/~nikolova/papers/stochWardropEqFinalOR.pdf </a></p>
<p>Earlier conference abstract: <a href="http://users.ece.utexas.edu/~nikolova/papers/SAGT2011-Paper39.pdf" target="_blank">http://users.ece.utexas.edu/~nikolova/papers/SAGT2011-Paper39.pdf </a></p>
<p>Technical summary: <a href="http://www.sigecom.org/exchanges/volume_11/1/NIKOLOVA.pdf" target="_blank">http://www.sigecom.org/exchanges/volume_11/1/NIKOLOVA.pdf </a></p>
</div></div></div><div class="field field-name-field-related-faculty field-type-node-reference field-label-inline clearfix"><div class="field-label">Related Faculty: </div><div class="field-items"><div class="field-item even"><a href="/people/faculty/evdokia-nikolova">Evdokia Nikolova</a></div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-inline clearfix"><div class="field-label">Keywords: </div><div class="field-items"><div class="field-item even"><a href="/tags/algorithmic-game-theory">Algorithmic Game Theory</a>, <a href="/tags/risk-aversion">Risk-aversion</a>, <a href="/tags/routing-under-uncertainty">Routing under uncertainty</a>, <a href="/tags/congestion">Congestion</a>, <a href="/tags/transportation-research">Transportation Research</a></div></div></div>Wed, 19 Mar 2014 21:32:03 +0000en47623412 at http://wncg.orghttp://wncg.org/research/briefs/traffic-assignment-uncertain-travel-times#comments