Last Wednesday evening I returned from EuroCG 2010 held in Dortmund, Germany. The weather was nice throughout the conference, and so were the food and drinks. (Although some people did not seem to care for the coffee in the lobby, but I’m not a coffee drinker.) Jan Vahrenhold and his team made this into a very smoothly run event, even in the presence of some unforeseen cancellations of talks.

A lot of interesting topics were presented in talks ranging in quality from moderate to excellent. I have to give special mention to Amit Chattopadhyay. When the speakers for the talk *2-Factor Approximation Algorithm for Computing Maximum Independent Set of a Unit Disk Graph*” could not attend the conference, he offered to give the talk instead of letting it get cancelled. Not being one of the authors, nor being affiliated with them, he just read their article and their slides a day in advance and gave a talk on-the-fly. Kudos!

## Fast-forward sessions

As decided by vote at the business meeting of EuroCG 2009, this year’s EuroCG was the first to have fast-forward sessions. In these short sessions, all conference attendees are together in one room. The speakers of the next two parallel sessions get 60 seconds each (with slides submitted in advance) to promote their talks. There is a coffee or lunch break before the actual parallel sessions start, and then the process repeats. This way, attendees are supposed to be able to make a more informed choice about which talks they want to attend.

This notion ~~stolen from~~ inspired by SIGGRAPH was still a bit unfamiliar to both organizers and speakers. During the first few fast-forward sessions the speakers were asked to go in “column order”, that is, first all the speakers of session A, then all speakers of session B. At the suggestion of several attendees, this was changed to “row order” so that “competing” speakers went one after another. This order was then kept for the rest of the conference.

In both orders, the speaker of session A always came before the parallel speaker of session B. This seemed unfair to me, but no one present seems to have used this to their benefit. More generally, I think most speakers (myself included) did not think the fast-forward through from a strategic point of view. My parallel speaker even had a slide with the title of our paper on it, saying something to the effect of “this guy is speaking in parallel to me, and his talk will surely also be nice”. Certainly a nice gesture , but I’m not entirely sure why someone would do this except to get a smaller audience.

All in all, I quite like the concept. Skimming the proceedings in advance says something of the topics, but not of the speakers. The addition of fast-forward sessions thus gives one this extra variable by which to decide which talks to attend. At the business meeting, the vote was *n*-3 against 3 in favor of keeping the fast-forward sessions, so they will be used again at EuroCG 2011 held in Morschach, Switzerland.

## Keynote speaker

Although all the invited speakers gave excellent talks, the one by Timothy Chan was the most memorable to me. With his inimitable enthusiasm he gave a one-hour talk on *Instance-Optimal Geometric Algorithms*.

He explained the concept using the example of computing 2D convex hulls. For some, “easy” sets *S* of *n* points there are algorithms to compute its *h* point convex hull in *O(n)* time, while for other, “hard” point sets different algorithms with a running time of *O(n *log* h)* are known to be optimal.

Timothy defined a function *H* (somewhat similar to entropy) so that *H(S)* is a number that measures how “hard” it is to compute the convex hull for point set *S*. More precisely, he proved that there is a *Ω(H(S))* lower bound for computing the 2D convex hull in the multilinear decision-tree model, by a simple and elegant adversary argument. He also showed that a slight modification of the Kirkpatrick-Seidel convex-hull algorithm yields a running time of *O(H(S))*. Thus its running time (up to constant factors) is as good or better than any other 2D convex hull algorithm that does not depend on the order of the points.

Timothy ended the talk with applications of the same technique to other problems, which in some cases did require new algorithms, such as for 3D convex hull. All in all a very impressive talk on some very impressive research, the paper for which can be found on Timothy’s website.

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