Machine Learning (Theory)

8/27/2009

New York Area Machine Learning Events

Several events are happening in the NY area.

  1. Barriers in Computational Learning Theory Workshop, Aug 28. That’s tomorrow near Princeton. I’m looking forward to speaking at this one on “Getting around Barriers in Learning Theory”, but several other talks are of interest, particularly to the CS theory inclined.
  2. Claudia Perlich is running the INFORMS Data Mining Contest with a deadline of Sept. 25. This is a contest using real health record data (they partnered with HealthCare Intelligence) to predict transfers and mortality. In the current US health care reform debate, the case studies of high costs we hear strongly suggest machine learning & statistics can save many billions.
  3. The Singularity Summit October 3&4. This is for the AIists out there. Several of the talks look interesting, although unfortunately I’ll miss it for ALT.
  4. Predictive Analytics World, Oct 20-21. This is stretching the definition of “New York Area” a bit, but the train to DC is reasonable. This is a conference of case studies of applications of ML to real-world problems.
  5. Machine Learning Symposium, Friday Nov. 6. I’m on the committee again this year. The abstract deadline is Sept. 30, and we already have several speakers lined up.

8/26/2009

Another 10-year paper in Machine Learning

When I was thinking about the best “10 year paper” for ICML, I also took a look at a few other conferences. Here is one from 10 years ago that interested me:

David McAllester PAC-Bayesian Model Averaging, COLT 1999. 2001 Journal Draft.

Prior to this paper, the only mechanism known for controlling or estimating the necessary sample complexity for learning over continuously parameterized predictors was VC theory and variants, all of which suffered from a basic problem: they were incredibly pessimistic in practice. This meant that only very gross guidance could be provided for learning algorithm design. The PAC-Bayes bound provided an alternative approach to sample complexity bounds which was radically tighter, quantitatively. It also imported and explained many of the motivations for Bayesian learning in a way that learning theory and perhaps optimization people might appreciate. Since this paper came out, there have been a number of moderately successful attempts to drive algorithms directly by the PAC-Bayes bound. We’ve gone from thinking that a bound driven algorithm is completely useless to merely a bit more pessimistic and computationally intense than might be necessary.

The PAC-Bayes bound is related to the “bits-back” argument that Geoff Hinton and Drew van Camp made at COLT 6 years earlier.

What other machine learning or learning theory papers from 10 years ago have had a substantial impact?

8/16/2009

Centmail comments

Tags: Economics,Problems jl@ 7:52 am

Centmail is a scheme which makes charity donations have a secondary value, as a stamp for email. When discussed on newscientist, slashdot, and others, some of the comments make the academic review process appear thoughtful :). Some prominent fallacies are:

  1. Costing money fallacy. Some commenters appear to believe the system charges money per email. Instead, the basic idea is that users get an extra benefit from donations to a charity and participation is strictly voluntary. The solution to this fallacy is simply reading the details.
  2. Single solution fallacy. Some commenters seem to think this is proposed as a complete solution to spam, and since not everyone will opt to participate, it won’t work. But a complete solution is not at all necessary or even possible given the flag-day problem. Deployed machine learning systems for fighting spam are great at taking advantage of a partial solution. The solution to this fallacy is learning about machine learning. In the current state of affairs, informed comment about spam fighting without knowing machine learning is difficult to imagine.
  3. Broken crypto fallacy. Some commenters seem to think that stamps can be reused arbitrarily on emails. This ignores the existence of strong hashes. The solution to this fallacy is simply checking the details and possibly learning about cryptographics hashes.

Dan Reeves made a very detailed FAQ trying to address all the failure modes seen in comments, and there is a bit more discussion at messy matters.

My personal opinion is that Centmail is an interesting idea that might work, avoids the failure modes of many other ideas, hasn’t failed yet, and hence is worth trying. It’s a better approach than my earlier thoughts on economic solutions to spam.

8/3/2009

Carbon in Computer Science Research

Tags: CS,Research jl@ 11:10 am

Al Gore‘s film and gradually more assertive and thorough science has managed to mostly shift the debate on climate change from “Is it happening?” to “What should be done?” In that context, it’s worthwhile to think a bit about what can be done within computer science research.

There are two things we can think about:

  1. Doing Research At a cartoon level, computer science research consists of some combination of commuting to&from work, writing programs, running them on computers, writing papers, and presenting them at conferences. A typical computer has a power usage on the order of 100 Watts, which works out to 2.4 kiloWatt-hours/day. Looking up David MacKay‘s reference on power usage per person, it becomes clear that this is a relatively minor part of the lifestyle, although it could become substantial if many more computers are required. Much larger costs are associated with commuting (which is in common with many people) and attending conferences. Since local commuting is common across many people, and there are known approaches (typically public transportation) for more efficient commuting, I expect researchers can piggyback on improvements in public transportation to reduce commuting costs. In fact, the situation for researchers may be better in general, as the nature of the job may make commuting avoidable, at least on some days.

    Presenting at conferences is the remaining problem area, essentially due to travel by airplane to and from a conference. Travel by airplane has an energy cost similar to travel by car over the same distance, but we typically take airplanes for very long distances. Unlike cars, typical airplane usage requires stored energy in a dense form. For example, there are no serious proposals I’m aware of for battery-powered airplanes, because all existing rechargeable batteries have a power density around 1/10th that of hydrocarbon fuel (which makes sense given that about 3/4 of the mass for a hydrocarbon fire is oxygen in the air). This suggests airplane transport may be particularly difficult to adapt towards low or zero carbon usage. The plausible approaches I know involve either using electricity (from where?) to inefficiently crack water for hydrogen, or the biofuel approach where hydrocarbons are made by plants, with neither of these approaches particularly far along in development. If these aren’t developed, it seems we should expect fewer conferences, more regional conferences, Europe with it’s extensive fast train network to be less impacted, and more serious effort towards distributed conferences. For the last, it’s easy to imagine with existing technology having simultaneous regional conferences which are mutually videoconferenced, and we aren’t far from being able to handle a fully interactive videobroadcast amongst an indefinitely large number of participants. As a corollary of fewer conferences, other interactive mechanisms (for example research blogs) seems likely to grow.

  2. Research Topics They keyword for research topics is efficiency, and it is not a trivial concern on a global scale. In computer science, there have been a few algorithms (such as quicksort and hashing) developed which substantially and broadly improved real-world efficiency, but the real driver of efficiency so far is the hardware development, which has phenomenally improved efficiency for several decades.

    Many of the efficiency improvements are sure to remain hardware based, but software is becoming an essential component. One basic observation about efficient algorithms is that for problems admitting an efficient parallel solution (counting is a great example), the parallel algorithm is generally more efficient, because energy use is typically superlinear in clock speed. As an extreme example, the human brain which is deeply optimized by evolution for energy efficiency typically runs at at 100Hz or 100KHz.

    Although efficiency suggests parallel algorithms, this should not be done blindly. For example, in machine learning the evidence I’ve seen so far suggests that online learning (which is admittedly harder to parallelize) is substantially more efficient than batch style learning, implying that I expect online approaches to be more efficient than map-reduce based machine learning as is typically seen in the Mahout project.

    A substantial difficulty with parallel algorithms is the programming itself. In this regard, there is plenty of room for programming language work as well.

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