Machine Learning (Theory)

1/7/2013

NYU Large Scale Machine Learning Class

Yann LeCun and I are coteaching a class on Large Scale Machine Learning starting late January at NYU. This class will cover many tricks to get machine learning working well on datasets with many features, examples, and classes, along with several elements of deep learning and support systems enabling the previous.

This is not a beginning class—you really need to have taken a basic machine learning class previously to follow along. Students will be able to run and experiment with large scale learning algorithms since Yahoo! has donated servers which are being configured into a small scale Hadoop cluster. We are planning to cover the frontier of research in scalable learning algorithms, so good class projects could easily lead to papers.

For me, this is a chance to teach on many topics of past research. In general, it seems like researchers should engage in at least occasional teaching of research, both as a proof of teachability and to see their own research through that lens. More generally, I expect there is quite a bit of interest: figuring out how to use data to make predictions well is a topic of growing interest to many fields. In 2007, this was true, and demand is much stronger now. Yann and I also come from quite different viewpoints, so I’m looking forward to learning from him as well.

We plan to videotape lectures and put them (as well as slides) online, but this is not a MOOC in the sense of online grading and class certificates. I’d prefer that it was, but there are two obstacles: NYU is still figuring out what to do as a University here, and this is not a class that has ever been taught before. Turning previous tutorials and class fragments into coherent subject matter for the 50 students we can support at NYU will be pretty challenging as is. My preference, however, is to enable external participation where it’s easily possible.

Suggestions or thoughts on the class are welcome :-)

1/1/2013

Deep Learning 2012

2012 was a tumultuous year for me, but it was undeniably a great year for deep learning efforts. Signs of this include:

  1. Winning a Kaggle competition.
  2. Wide adoption of deep learning for speech recognition.
  3. Significant industry support.
  4. Gains in image recognition.

This is a rare event in research: a significant capability breakout. Congratulations are definitely in order for those who managed to achieve it. At this point, deep learning algorithms seem like a choice undeniably worth investigating for real applications with significant data.

7/11/2011

Interesting Neural Network Papers at ICML 2011

Maybe it’s too early to call, but with four separate Neural Network sessions at this year’s ICML, it looks like Neural Networks are making a comeback. Here are my highlights of these sessions. In general, my feeling is that these papers both demystify deep learning and show its broader applicability.

The first observation I made is that the once disreputable “Neural” nomenclature is being used again in lieu of “deep learning”. Maybe it’s because Adam Coates et al. showed that single layer networks can work surprisingly well.

Another surprising result out of Andrew Ng’s group comes from Andrew Saxe et al. who show that certain convolutional pooling architectures can obtain close to state-of-the-art performance with random weights (that is, without actually learning).

Of course, in most cases we do want to train these models eventually. There were two interesting papers on the topic of training neural networks. In the first, Quoc Le et al. show that a simple, off-the-shelf L-BFGS optimizer is often preferable to stochastic gradient descent.

Secondly, Martens and Sutskever from Geoff Hinton’s group show how to train recurrent neural networks for sequence tasks that exhibit very long range dependencies:

It will be interesting to see whether this type of training will allow recurrent neural networks to outperform CRFs on some standard sequence tasks and data sets. It certainly seems possible since even with standard L-BFGS our recursive neural network (see previous post) can outperform CRF-type models on several challenging computer vision tasks such as semantic segmentation of scene images. This common vision task of labeling each pixel with an object class has not received much attention from the deep learning community.
Apart from the vision experiments, this paper further solidifies the trend that neural networks are being used more and more in natural language processing. In our case, the RNN-based model was used for structure prediction. Another neat example of this trend comes from Yann Dauphin et al. in Yoshua Bengio’s group. They present an interesting solution for learning with sparse bag-of-word representations.

Such sparse representations had previously been problematic for neural architectures.

In summary, these papers have helped us understand a bit better which “deep” or “neural” architectures work, why they work and how we should train them. Furthermore, the scope of problems that these architectures can handle has been widened to harder and more real-life problems.

Of the non-neural papers, these two papers stood out for me:

8/23/2010

Boosted Decision Trees for Deep Learning

Tags: Deep,Machine Learning,Supervised jl@ 11:18 am

About 4 years ago, I speculated that decision trees qualify as a deep learning algorithm because they can make decisions which are substantially nonlinear in the input representation. Ping Li has proved this correct, empirically at UAI by showing that boosted decision trees can beat deep belief networks on versions of Mnist which are artificially hardened so as to make them solvable only by deep learning algorithms.

This is an important point, because the ability to solve these sorts of problems is probably the best objective definition of a deep learning algorithm we have. I’m not that surprised. In my experience, if you can accept the computational drawbacks of a boosted decision tree, they can achieve pretty good performance.

Geoff Hinton once told me that the great thing about deep belief networks is that they work. I understand that Ping had very substantial difficulty in getting this published, so I hope some reviewers step up to the standard of valuing what works.

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