Mainly storing a link to this interesting paper that raises some questions:

William Press, "Strong profiling is not mathematically optimal for discovering rare malfeasors".  Weak profiling apparently is---under the assumptions of his model, which seem to me a rather imperfect fit, but not wholly irrelevant, to most real-world terrorist-screening scenarios.   No implied view from me on the correctness or relevance of these results, pending more careful reading and thought.

Aha, just realized it's that Bill Press--former (pre-2004) deputy director for Science and Technology at LANL (curently at UT Austin, on leave from LANL).

Oh yeah, link is from The Yorkshire Ranter, who got it from Bruce Schneier.

Nice point by Seth Godin on how to see if someone really knows what they're talking about.  I see it in my field too---people judging by the extent to which one can carry on an extemporaneous conversation about the subject at hand, revealing months of thought about the topic at hand, years of study of the background issues.  On the other hand, we also need --- sorely, and in my opinion, even in technical fields --- people with breadth---non-superficial breadth, to be sure.  How does one spot that?

I must store some references to good recent talks, in part so I don't forget them:

Two talks by Tsuyoshi Ito:  an IQC theory lunch talk about how the complexity class defined by interactive proof systems with two provers who may share *arbitrary non-signaling correlations* (rather than just quantum ones) with each other, turns out to be PSPACE.  Communication between verifier and provers is classical.  This is the same class as that defined by quantum interactive proof systems (for any fixed number of provers, but *without* shared correlations, quantum or otherwise)---a result due (at least the hard direction, that PSPACE is contained in QIP) to Jain, Ji, Upadhyay, and Watrous).  Very nice stuff.  (Note that as far as I know it doesn't imply that two-prover proof systems with classical communication between verifier and provers, but verifiers sharing quantum entanglement, is in PSPACE.  Although this latter model gives the verifiers, collectively, strictly less power, the reduction in their collective power could increase the power of the proof system:  crudely speaking, the provers might have less power to attempt to coordinate in bamboozling the verifier into wrongly accepting.

The really kooky, like me, might ask, what if we allow the communication between verifiers and provers to involve exchanging the kinds of systems involved in the provers' shared non-signaling correlations.  "Popescu-Rohrlich bits", or generalizations involving larger numbers of outcomes per measurement, and larger numbers of measurements.  (States of "semiclassical test spaces", in a different lingo.)

Tsuyoshi's other talk was an informal one at the quantum information group meeting at PI, about XOR games with more than two players.  More on it later.

A few weeks ago Stephanie Wehner gave us a lovely informal quantum foundations seminar on a recent paper she wrote with Jonathan Oppenheim, whose thesis is that if quantum theory were more nonlocal it would violate uncertainty relations.  The uncertainty relations involved are a new type she (and Andreas Winter?) introduced, called "finegrained uncertainty relations".  I'll try to summarize this talk in a later post, too.

US Brigadier General H.R. McMaster, who's led combat forces in Iraq:

"Some problems aren't bullet-izable."

He was explaining why he'd banned PowerPoint presentations while "leading the successful effort to secure the northern Iraqi city of Tal Afar in 2005."    Quoted in article in the New York Times.

Just a link to Vazirani's guest post on Noam Nisan's blog Algorithmic Game Theory, which seems to relate to my interest in convex sets with beautiful structure.  (Homogeneous self-dual cones, like the positive semidefinite matrices (semidefinite programming) or the positive orthant (linear programming);  just plain homogeneous cones; hyperbolicity cones...; just plain self-dual cones; weakly self-dual cones (ones isomorphic to their dual, but for which no inner product on the space can make the dual (defined according to said inner product) equal to the cone itself), etc...).  And a thought, perhaps misguided:  isn't a crucial ingredient of an efficient algorithm for a convex program usually something like an efficient algorithm for something like: determining membership in the convex set, or calculating a nice barrier function for the set?  And doesn't the ability to do that usually depend on the set (and/or the cone it generates) having a "nice" structure?  Perhaps the detailed properties of this structure bears some relation to the "combinatorial" structure of algorithms like the Ford-Fulkerson algorithm for max-flow?  Or perhaps particular problems have additional structure that isn't being captured in a typical convex formulation.  I'm no expert here (and have indeed forgotten what the Ford-Fulkerson algorithm is, though I think I once read about it in a book by Vazirani).  This post is primarily to remind myself to look at this more closely---and to link to Vazirani's, which seems worth of attention.

The horns and cheers are sounding in my house a block off the main street (King street) of uptown Waterloo.  I watched the end of the US-Canada hockey game in a pub, the Fox and Fiddle, on King street and it was a hard-fought thriller.  I'm happy for Canada, and they're sure as heck happy! The US team fought hard and has nothing to be ashamed of---but you could see the disappointment in their faces afterward, though they were absolutely sportsmanlike about it.

King street near the major pubs is lined with people hugging each other, high-fiving, waving canadian flags, and stopping passing motorists to high-five them as well.  After a Candian lead of 2-1 held for a long time, the US, which had been playing strongly and getting plenty of time with the puck, made a tieing goal with about 20 seconds left.  In a really hard-fought overtime, Canada sunk a sudden-death goal for the gold.  With that medal, they now have the most gold medals any country has won in a single winter olympics, said the commentators on CBC TV.

There was a lot of spirit in the pub, and I realized I was dressed in black, grey and blue from head to toe---not a spot of red except on my red, grey, and blue hat.  (Or should that be tuque?)  No issues, though---I am not a hugely vocal sports fan and don't normally watch hockey---though somehow the guy who was going 'round hugging everyone in the pub took a look and gave me a miss.  I walked up and down King street to check out the scene, and ended up having to high-five a few people and clap one person on the back, all with a "Congratulations!" which presumably marked me as not Canadian.    (A Canadian would yell "Canada, yeeeaaaaaaaah!!!"., as about five hundred are doing a block or two away right now.)

I did see one ambulance turn the corner onto King, lights flashing.  Keep it safe out there, guys and gals.  Don't drink and drive, don't get into fast traffic, etc...  (Fifteen minutes after the victory, after the medal ceremony, a group in the pub raised a chant of "Let's get wasted!".)

I had a pint of Molson's Canadian Lager during the overtime.  The drink of the Canadian women's hockey team, it was clear, smooth, and tasty, and really hit the spot.  No cigars today, though---although I suppose up here you can get real Cubans.  (Now there would be a provocative way to celebrate a US win!)

I'm glad it was a really hard-fought game, with everyone playing their best, and I don't think anybody should feel bad about their performance.   Great job all around, and a smashing finish for the Canadians to a great olympics!

It's getting louder out there.  Hopefully I can find my camera and post some pics of the celebration.

Edit:  didn't find my camera, but Youtubers provide more than enough flavor of the scene:

Interesting-looking bit of political economy research.  They propose that sectors employing lower-earning workers more intensively are receive relatively more trade protection, based on research in the US and China, and apparently attempt to differentiate between the contributions of envy and altruism to this effect.  Also, presumably, compare it to theories where amount of protection depends primarily on the resources available to an industry to help secure it.  NBER charges five bucks (OK, that beats Springer journals hands-down, but still) to download, so unless PI gets a subscription, looks like I'm not reading it.  What is with charging money for working papers!?  Can't we get these economists on the arXiv???

Proving that Proving is Hard.  Computer scientist Dick Lipton gives a beautiful introduction to work by Fischer and Rabin on the computational complexity of the formal first-order theory of the real numbers.  As Lipton explains, Alfred Tarski showed that this theory is complete---that every well-formed statement in the language of the theory can either be proved, or be disproved, from the axioms of the theory. Fischer and Rabin investigated how hard it can be to prove statements in the theory.   According to Lipton, they showed that it's (worst-case) exponentially hard:  there is a positive constant $c$ such that there are true sentences of the theory, of length shorter than $n$, whose shortest proof has length at least $2^{cn}$.  (I'd guess what's meant is that they show this holds for all large enough $n$, or at least for an infinite set of $n$.)

Quantifier elimination---the method of deciding statements in the theory of the reals, used by Tarski in his decidability proof---has, at least theoretically, applications in optimization, which I hope to delve into in a future post.

A nice, probably not-too-easy (for me) and not-too-hard problem in group theory from my colleague Alberto Montina: is $SU(N-1)$ a subgroup of $SU(N)$ of maximal dimension (as a manifold) and are there any others.

Paul Halmos, How to Write Mathematics.

Amazing interview with Eugene Fama who doesn't believe the present crisis is due to the bursting of a bubble in housing:  "That’s where economics has always broken down. We don’t know what causes recessions. Now, I’m not a macroeconomist so I don’t feel bad about that. (Laughs again.) We’ve never known. Debates go on to this day about what caused the Great Depression. Economics is not very good at explaining swings in economic activity."  (Link found on Paul Krugman's blog. )

And an interesting bit about consumption and healthcare from something called Left Business Observer (link found on Brad Delong's blog).  The basic point is that of the six percentage point rise in what the national-income accounts categorize as consumption, as a share of GDP (from around 64 in the 80's to around 70% in 2007 and 2008), about four percentage points are in health care.

More wine from Perimeter Institute's bistro:  at today's wine and cheese, a Slowine Syrah from South Africa (didn't catch the vintage, maybe 2008?) was quite nice, smooth and tasty.  The 2007 Closson Chase South Clos Chardonnay was remarkable...obviously unfiltered, deeply colored for a chardonnay, and tasting unfiltered as well.  Their chardonnays are some of bistro manager Dan Lynch's favorite wines, and this was a chance to taste a little of something quite special.  The winery, and I believe also the vineyard for this wine, is in Prince Edward County, a large peninsula that's nearly an island, in a relatively sparsely populated part of the North shore of Lake Ontario, about two-thirds of the way from Toronto to Kingston.  The wine is barrel fermented (in 25% new oak, 75% old, in a typical  year, according to their website), and as a result noticeably oaky.  It's also not so high in acid or racy as one might expect from a high-end chardonnay (then again 2007 yielded exceptionally ripe grapes most places in Ontario, I think) but very "natural-tasting"--grapey, slightly sweet but not in a cloying way, with deep flavor underlying the oak.  I don't really feel like doing the tutti frutti thing with the flavors---it tasted mostly like ripe chardonnay grapes.  I guess someone might say it had hints of fruitcake.  The wine, that is, the wine.  This will be interesting to watch over the years as the flavors integrate with the oak in the bottle.  Really made the case for unfiltered chardonnay, for me---even the appearance in the glass is so much more interesting than just a clear liquid.  Slight question marks perhaps, on whether there is a tad too much oak, and whether it has enough acid to age gracefully, but I think the strong fruit and relaxed, natural style render these questions moot.  Bottom line: I want more, and will take steps to secure some if possible.

Incidentally, yesterday at PI's pub night  I had the Pillitteri standard (i.e. non-reserve) 2007 Merlot again, and liked it better this time.  It was served in one of the tall, big-bowled Riedel restaurant glasses, and seemed more elegant and velvety.  Perhaps a case of the glass influencing perception, or maybe it was the extra room in the glass for the aromas to develop  (and the schnozz to dip into them), or maybe it was just a different bottle or an extra month's age.  Still not earthshaking, but a solid, enjoyable drink.

What with pub night and wine 'n cheese, I realize I'm making PI sound like a boozefest, but pub night mostly means inexpensive food (and beer, to be sure), and is very family-oriented---a welcome chance to socialize with non-physicists.  And, hey, after my two glasses at wine and cheese, I went back to my office and LaTeX'd up five pages or so on tensor products of JC algebras.  So we're not slacking off here, or anything.  The bistro and the science are synergetic...