Archive for the ‘Hidden Markov Model’ Category

Foundations of Data Science

Sunday, September 29th, 2013

Foundations of Data Science by John Hopcroft and Ravindran Kannan.

From the introduction:

Computer science as an academic discipline began in the 60’s. Emphasis was on programming languages, compilers, operating systems, and the mathematical theory that supported these areas. Courses in theoretical computer science covered nite automata, regular expressions, context free languages, and computability. In the 70’s, algorithms was added as an important component of theory. The emphasis was on making computers useful. Today, a fundamental change is taking place and the focus is more on applications. There are many reasons for this change. The merging of computing and communications has played an important role. The enhanced ability to observe, collect and store data in the natural sciences, in commerce, and in other elds calls for a change in our understanding of data and how to handle it in the modern setting. The emergence of the web and social networks, which are by far the largest such structures, presents both opportunities and challenges for theory.

While traditional areas of computer science are still important and highly skilled individuals are needed in these areas, the majority of researchers will be involved with using computers to understand and make usable massive data arising in applications, not just
how to make computers useful on specifi c well-defi ned problems. With this in mind we have written this book to cover the theory likely to be useful in the next 40 years, just as automata theory, algorithms and related topics gave students an advantage in the last 40 years. One of the major changes is the switch from discrete mathematics to more of an emphasis on probability, statistics, and numerical methods.

In draft form but impressive!

Current chapters:

  1. Introduction
  2. High-Dimensional Space
  3. Random Graphs
  4. Singular Value Decomposition (SVD)
  5. Random Walks and Markov Chains
  6. Learning and the VC-dimension
  7. Algorithms for Massive Data Problems
  8. Clustering
  9. Topic Models, Hidden Markov Process, Graphical Models, and Belief Propagation
  10. Other Topics [Rankings, Hare System for Voting, Compressed Sensing and Sparse Vectors]
  11. Appendix

I am certain the authors would appreciate comments and suggestions concerning the text.

I first saw this in a tweet by CompSciFact.

Probabilistic Graphical Models (class)

Monday, November 21st, 2011

Probabilistic Graphical Models (class) by Daphne Koller. (Stanford University)

From the web page:

What are Probabilistic Graphical Models?

Uncertainty is unavoidable in real-world applications: we can almost never predict with certainty what will happen in the future, and even in the present and the past, many important aspects of the world are not observed with certainty. Probability theory gives us the basic foundation to model our beliefs about the different possible states of the world, and to update these beliefs as new evidence is obtained. These beliefs can be combined with individual preferences to help guide our actions, and even in selecting which observations to make. While probability theory has existed since the 17th century, our ability to use it effectively on large problems involving many inter-related variables is fairly recent, and is due largely to the development of a framework known as Probabilistic Graphical Models (PGMs). This framework, which spans methods such as Bayesian networks and Markov random fields, uses ideas from discrete data structures in computer science to efficiently encode and manipulate probability distributions over high-dimensional spaces, often involving hundreds or even many thousands of variables. These methods have been used in an enormous range of application domains, which include: web search, medical and fault diagnosis, image understanding, reconstruction of biological networks, speech recognition, natural language processing, decoding of messages sent over a noisy communication channel, robot navigation, and many more. The PGM framework provides an essential tool for anyone who wants to learn how to reason coherently from limited and noisy observations.

About The Course

In this class, you will learn the basics of the PGM representation and how to construct them, using both human knowledge and machine learning techniques; you will also learn algorithms for using a PGM to reach conclusions about the world from limited and noisy evidence, and for making good decisions under uncertainty. The class covers both the theoretical underpinnings of the PGM framework and practical skills needed to apply these techniques to new problems. Topics include: (i) The Bayesian network and Markov network representation, including extensions for reasoning over domains that change over time and over domains with a variable number of entities; (ii) reasoning and inference methods, including exact inference (variable elimination, clique trees) and approximate inference (belief propagation message passing, Markov chain Monte Carlo methods); (iii) learning methods for both parameters and structure in a PGM; (iv) using a PGM for decision making under uncertainty. The course will also draw from numerous case studies and applications, so that you’ll also learn how to apply PGM methods to computer vision, text understanding, medical decision making, speech recognition, and many other areas.

Another very strong resource from Stanford.

Serious (or aspiring) data miners will be lining up for this course!

A Variational HEM Algorithm for Clustering Hidden Markov Models

Monday, September 12th, 2011

A Variational HEM Algorithm for Clustering Hidden Markov Models by: Emanuele Coviello, Antoni B. Chan, and Gert R.G. Lanckriet.

Abstract:

The hidden Markov model (HMM) is a generative model that treats sequential data under the assumption that each observation is conditioned on the state of a discrete hidden variable that evolves in time as a Markov chain. In this paper, we derive a novel algorithm to cluster HMMs through their probability distributions. We propose a hierarchical EM algorithm that i) clusters a given collection of HMMs into groups of HMMs that are similar, in terms of the distributions they represent, and ii) characterizes each group by a “cluster center”, i.e., a novel HMM that is representative for the group. We present several empirical studies that illustrate the benefits of the proposed algorithm.

Warning: Heavy sledding but the examples of improved hierarchical motion clustering, music tagging, and online hand writing recognition are quite compelling.

Shogun – Google Summer of Code 2011

Sunday, April 3rd, 2011

Shogun – Google Summer of Code 2011

Students! Here is your change to work on a cutting edge software library for machine learning!

Posted ideas, or submit your own.

From the website:

SHOGUN is a machine learning toolbox, which is designed for unified large-scale learning for a broad range of feature types and learning settings. It offers a considerable number of machine learning models such as support vector machines for classification and regression, hidden Markov models, multiple kernel learning, linear discriminant analysis, linear programming machines, and perceptrons. Most of the specific algorithms are able to deal with several different data classes, including dense and sparse vectors and sequences using floating point or discrete data types. We have used this toolbox in several applications from computational biology, some of them coming with no less than 10 million training examples and others with 7 billion test examples. With more than a thousand installations worldwide, SHOGUN is already widely adopted in the machine learning community and beyond.

SHOGUN is implemented in C++ and interfaces to MATLAB, R, Octave, Python, and has a stand-alone command line interface. The source code is freely available under the GNU General Public License, Version 3 at http://www.shogun-toolbox.org.

This summer we are looking to extend the library in four different ways: Improving interfaces to other machine learning libraries or integrating them when appropriate, improved i/o support, framework improvements and new machine algorithms. Here is listed a set of suggestions for projects.

A prior post on Shogun.

Which Automatic Differentiation Tool for C/C++?

Tuesday, February 8th, 2011

Which Automatic Differentiation Tool for C/C++?

OK, not immediately obvious why this is relevant to topic maps.

Nor is Bob Carpenter’s references:

I’ve been playing with all sorts of fun new toys at the new job at Columbia and learning lots of new algorithms. In particular, I’m coming to grips with Hamiltonian (or hybrid) Monte Carlo, which isn’t as complicated as the physics-based motivations may suggest (see the discussion in David MacKay’s book and then move to the more detailed explanation in Christopher Bishop’s book).

particularly useful.

I suspect the two book references are:

but I haven’t asked. In part to illustrate the problem of resolving any entity reference. Both authors have authored other books touching on the same subjects so my guesses may or may not be correct.

Oh, relevance to topic maps. The technique automatic differentiation is used in Hamiltonian Monte Carlo methods for the generation of gradients. Still not helpful? Isn’t to me either.

Ah, what about Bayesian models in IR? That made the light go on!

I will be discussing ways to show more immediate relevance to topic maps, at least for some posts, in post #1000.

It isn’t as far away as you might think.

PyBrain: The Python Machine Learning Library

Thursday, February 3rd, 2011

PyBrain: The Python Machine Learning Library

From the website:

PyBrain is a modular Machine Learning Library for Python. Its goal is to offer flexible, easy-to-use yet still powerful algorithms for Machine Learning Tasks and a variety of predefined environments to test and compare your algorithms.

PyBrain is short for Python-Based Reinforcement Learning, Artificial Intelligence and Neural Network Library. In fact, we came up with the name first and later reverse-engineered this quite descriptive “Backronym”.

How is PyBrain different?

While there are a few machine learning libraries out there, PyBrain aims to be a very easy-to-use modular library that can be used by entry-level students but still offers the flexibility and algorithms for state-of-the-art research. We are constantly working on more and faster algorithms, developing new environments and improving usability.

What PyBrain can do

PyBrain, as its written-out name already suggests, contains algorithms for neural networks, for reinforcement learning (and the combination of the two), for unsupervised learning, and evolution. Since most of the current problems deal with continuous state and action spaces, function approximators (like neural networks) must be used to cope with the large dimensionality. Our library is built around neural networks in the kernel and all of the training methods accept a neural network as the to-be-trained instance. This makes PyBrain a powerful tool for real-life tasks.

Another tool kit to assist in the construction of topic maps.

And another likely contender for the Topic Map Competition!

MALLET: MAchine Learning for LanguagE Toolkit
Topic Map Competition (TMC) Contender?

Thursday, February 3rd, 2011

MALLET: MAchine Learning for LanguagE Toolkit

From the website:

MALLET is a Java-based package for statistical natural language processing, document classification, clustering, topic modeling, information extraction, and other machine learning applications to text.

MALLET includes sophisticated tools for document classification: efficient routines for converting text to “features”, a wide variety of algorithms (including Naïve Bayes, Maximum Entropy, and Decision Trees), and code for evaluating classifier performance using several commonly used metrics.

In addition to classification, MALLET includes tools for sequence tagging for applications such as named-entity extraction from text. Algorithms include Hidden Markov Models, Maximum Entropy Markov Models, and Conditional Random Fields. These methods are implemented in an extensible system for finite state transducers.

Topic models are useful for analyzing large collections of unlabeled text. The MALLET topic modeling toolkit contains efficient, sampling-based implementations of Latent Dirichlet Allocation, Pachinko Allocation, and Hierarchical LDA.

Many of the algorithms in MALLET depend on numerical optimization. MALLET includes an efficient implementation of Limited Memory BFGS, among many other optimization methods.

In addition to sophisticated Machine Learning applications, MALLET includes routines for transforming text documents into numerical representations that can then be processed efficiently. This process is implemented through a flexible system of “pipes”, which handle distinct tasks such as tokenizing strings, removing stopwords, and converting sequences into count vectors.

An add-on package to MALLET, called GRMM, contains support for inference in general graphical models, and training of CRFs with arbitrary graphical structure.

Another tool to assist in the authoring of a topic map from a large data set.

It would be interesting but beyond the scope of the topic maps class, to organize a competition around several of the natural language processing packages.

To have a common data set, to be released on X date, with topic maps due say within 24 hours (there is a TV show with that in the title or so I am told).

Will have to give that some thought.

Could be both interesting and entertaining.

Probabilistic User Modeling in the Presence of Drifting Concepts

Saturday, December 4th, 2010

Probabilistic User Modeling in the Presence of Drifting Concepts Authors(s): Vikas Bhardwaj, Ramaswamy Devarajan

Abstract:

We investigate supervised prediction tasks which involve multiple agents over time, in the presence of drifting concepts. The motivation behind choosing the topic is that such tasks arise in many domains which require predicting human actions. An example of such a task is recommender systems, where it is required to predict the future ratings, given features describing items and context along with the previous ratings assigned by the users. In such a system, the relationships among the features and the class values can vary over time. A common challenge to learners in such a setting is that this variation can occur both across time for a given agent, and also across different agents, (i.e. each agent behaves differently). Furthermore, the factors causing this variation are often hidden. We explore probabilistic models suitable for this setting, along with efficient algorithms to learn the model structure. Our experiments use the Netflix Prize dataset, a real world dataset which shows the presence of time variant concepts. The results show that the approaches we describe are more accurate than alternative approaches, especially when there is a large variation among agents. All the data and source code would be made open-source under the GNU GPL.

Interesting because not only do concepts drift from user to user but modeling users as existing in neighborhoods of other users was more accurate than purely homogeneous or heterogeneous models.

Questions:

  1. If there is a “neighborhood” effect on users, what, if anything does that imply for co-occurrence of terms? (3-5 pages, no citations)
  2. How would you determine “neighborhood” boundaries for terms? (3-5 pages, citations)
  3. Do “neighborhoods” for terms vary by semantic domains? (3-5 pages, citations)

*****
Be aware that the Netflix dataset is no longer available. Possibly in response to privacy concerns. A demonstration of the utility of such concerns and their advocates.