Research Areas

Machine Learning

Emphasizing theory and algorithms for learning from high-dimensional data, and reasoning under uncertainty.

Computational Biology

Emphasizing developing formal models and algorithms that address problems of practical biological and medical concerns.

  • Learning time & space varying-coefficient models with evolving structures, & applications in sociocultural data mining & systems biology [more]
  • Learning sparse structured input/output models in very high-dimensional space, & applications in structured prediction problems in NLP, vision, & bioinformatics [more]
  • Statistical models & algorithms of networks & relational data [more]
  • Nonparametric Bayesian analysis, applications of Bayesian nonparametrics in data mining [more]
  • Dynamic topic models for structured browsing of large corpus of text/image/video/network data [more]
  • Other applications of probabilistic graphical models in Computational Biology, IR, NLP, Multimedia & Control [more]
  • Genome-Transcription-Phenome-Wide Association: a new paradigm for association studies in complex diseases [more]
  • Recovering and exploring time-varying gene interactions in Drosophila development & human disease progression [more]
  • Computational systems biology of genome-microenvironment interactions in breast cancer [more]
  • Probabilistic evolutionary models of cis-regulatory modules in Drosophila [more]
  • Inference of population genetic structure, variation, migration, & evolution based on genome polymorphisms [more]
  • Biological sequence analysis: motif detection, gene finding & systems biology [more]

 

Machine Learning

Emphasizing theory and algorithms for learning complex probabilistic models, learning with prior knowledge, and reasoning under uncertainty.

 

Learning Time and Space Varying-Coefficient Models with Evolving Structures, and Applications in Socio-cultural Data Mining and Systems Biology

In this project we develop methodologies for estimating and analyzing varying-coefficient models with structural changes occurring at unknown times or locations. Instances of such models are frequently encountered in social and biological problems where data are structured and longitudinal, and the iid assumptions on sample with respect to an invariant underlying model no longer hold. For example, at each time point, the observation (such as a single snapshot of social state of all actors) is distributed according to a model (such as a network) specific to that time, and therefore can not be directly used for estimating models underlying other time points. The main issues we concern in this project include estimating the changing model structures and parameters, number of structural changes, the change times, and the unknown coefficient functions. We will develop efficient and scalable algorithms for addressing these problems under "small n large p" scenarios based on techniques such as sparse regression under various regularization and structured-constraint schemes, convex optimization, and Bayesian inference. We will also focus on asymptotic analysis of the procedure and give conditions under which it is able to correctly estimate the structural changes and the model coefficients.

Selected Reading:

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Learning Sparse Structured Input/Output Models in Very High-dimensional Space, and Applications in Structured prediction problems in NLP, Vision, and Bioinformatics

In many high-dimensional structured I/O problems, such as genome-phenome association analysis and image segmentation, where both input and output can contain tens of thousands, sometimes even millions of inter-related features, learning a sparse and consistent structured predictive function can be of paramount importance for both robustness and interpretability of the model. In this project, we attack this problem from two directions. One direction we will pursue to learn sparse structured I/O models is to extend the l1-regularized regression model (i.e., the lasso method) to a family of sparse "structured" regression models in the contexts of uncovering true associations between linked genetic variations (inputs) and networked phenotypes (outputs), which can be cast as efficiently solvable convex optimization problems and yield parsimonious and possibly consistent maximum likelihood estimates of the model. Another direction we are exploring is based on a new statistical formalism known as the maximum entropy discrimination Markov networks, which address the problem of estimating sparse structured I/O models under a maximum margin framework, but using a entropic regularizer that leads to a distribution of structured prediction functions that are simultaneously primal and dual sparse (i.e., with few support vectors, and of low effective feature dimension), and can be efficiently solved via a novel algorithm that builds on variational inference and existing solvers for the maximum margin Markov network (which is a special case of our proposed model). We will also investigate the theoretical guarantee of these methods such as generalization bounds, sample complexity, convergence behavior.

Selected Reading

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Statistical Models and Algorithms of Networks and Relational Data (in collaboration with Stephen Fienberg)

A plausible representation of the relational information among entities in dynamic systems such as a living cell, or a social community, or the internet, is a stochastic network which is topologically rewiring and semantically evolving over time (or space). In this project we develop probabilistic generative models for the formation, growth, evolution, and dynamics of networks and relational data in general, and inference/learning algorithms for node labeling, link prediction, latent theme extraction, etc., for network and relational data. We also work on theoretical issues, such as bounds, complexity, related to our models and algorithms, and applications to the analysis of socio-cultural networks, author-citation networks, the blogosphere, and biological networks.

Selected Reading

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Bayesian statistics, nonparametric Bayesian analysis, algorithms and applications of Bayesian nonparametrics in data mining

In this project we develop nonparametric and semiparametric Bayesian models (based on the Dirichlet process and extensions, sometimes known as the generalized Polya urn schemes) for analyzing time series data, hierarchical data, and other complex inputs with uncertain internal structure, which arise from temporal text mining (e.g., emails, news streams), object tracking (e.g., video surveillance, navigation and control) and biological data analysis. We develop formal probabilistic formalisms, sampling and variational inference algorithms, and also address theoretical issues such as consistence, bounds and convergence of our models and algorithms.

Selected Reading

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Dynamic topic models for structured browsing of large corpus of text/image/video/network data

This is a "google-style" project in which we develop formal methods for visualizing, categorizing, and tracking content-rich multimedia and network data-streams in an arbitrary-dimension "tomographic" space of latent semantic topics, where each entity can be represented by a human-perceivable and interpretable "semantic" coordinates or trajectory, so that one can succinctly browse the complex multimodal and time-evolving data in a direct, global and on-line fashion. Such display of complex data complements the current Google representation of web-information, which is one-dimensional (in terms of a rank list), static (no change in the topical content of the media can be traced), and unimodal (only one type of media can be displayed as a time, such as text only, or image only). One can use our system to directly visualize in the topic space a much larger amount of media or web information, rather than via pages of ordered-lists of subjects as in current Google interface. One can detect bias, ideological perspective, or other subtle information, which hide beneath the topical contents in news article or other media. One can directly measure (by eye) the distance between query and related entities rather than following a rank list, which offer more flexibility and higher accuracy. One can also track the trajectories of evolving entities and detection events such as birth/death of themes/topics using our system, which is not possible under Google.

Selected Reading

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Other applications of probabilistic graphical models in Computational Biology, IR, NLP, Multimedia and Control (in collaboration with many faculty and students at CMU and other universities)

We design various task-specific generative, discriminative, and hybrid graphical models and algorithms for various biological and genetic problems (see bellow), for NLP problems such as statistical machine translation, for comprehending and categorizing text corpus, for segmenting, tracking and interpreting video and caption streams from various sources (e.g., surveillance system, robots), and for decision making and active learning in dynamic environments.

Selected Reading

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Computational Biology

With an emphasis on developing formal models and algorithms that address problems of practical biological and medical concerns.

 

Genome-Transcription-Phenome-Wide Association: a new paradigm for association studies in complex diseases (in collaboration with various faculty in UPMC and Harvard Medical School)

Many complex disease syndromes consist of a large number of related, rather than independent, clinical phenotypes. Differences between these syndromes involve the complex interplay of a large number of genomic variations that perturb the function of disease-related genes in the context of a regulatory network, rather than individually. The current state-of-the-art in genome-wide-association studies (GWAS) is a single-gene association approach. A major challenge for the immediate future is therefore to transcend the one-gene/one-disease approach with a suite of approaches that account for pathway and network structure. In this project, we aim at developing algorithms and software to enable next-generation association analysis addressing these problems, in the context of asthma disease. We are developing methodologies for the largely unexplored but practically important problem of structured associations between elements in the genome, transcriptome, and the phenome. This research will open a new paradigm for association studies of complex diseases, which facilitates: 1) Intra- and inter-omic integration of data for association mapping and disease gene/pathway discovery, 2) Thorough explorations of the internal structures within different omic data, so that cryptic associations that are not possibly detectable in unstructured analysis due to their weak statistical power can be now inferred. 3) Joint statistical inference of mechanisms and pathways of how variations in DNA lead to variations in complex traits flows through molecular networks, and inference of condition-specific state of gene function in the molecular networks, and 4) Development of faster and automated computational algorithm with greater scalability and robustness to large-scale inter-omic analysis, and more convenient software package and user interface.

Selected Reading

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Recovering and Exploring Time-Varying Gene Interactions in Drosophila Development and Human Disease Progression (in collaboration with various faculty in University of Chicago and Harvard Medical School)

Due to the dynamic nature of biological systems, biological networks underlying temporal process such as development, immunoresponse, and disease progression can exhibit significant topological changes to facilitate dynamic regulatory functions. The latent functionality or membership undertaken by the biomolecules as determined by these dynamic interactions will also exhibit rich temporal behaviors, assuming a distinct function at one point while leaning more towards a second function at an another point. In this project, we focus on two dynamic processes, the life cycle of Drosophila melanogaster, and the progress of asthma in human, for which we develop methodologies to, 1) reverse-engineer latent time-evolving gene networks based on either microimages of spatial pattern of gene expressions in Drosophila embryos, or genome-wide microarray profile of gene expression intensities; 2) recover the transcriptional activation/repression functions from temporal/spatial patterns of gene expressions; 3) estimate embeddings of every genes into a latent function space and track its mixed membership of functions in the latent space across time. The goal is to understand the driving forces underlying dynamic rewiring of gene regulation circuity, and to predict future network structures.

Selected Reading

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Computational systems biology of genome-microenvironment interactions in breast cancer (in collaboration with Mina Bissell)

In this project we analyze the molecular abundance profiles (e.g., microarray, CGH, ChIp-Chip) measured in a "designer microenvironment", realized in 3D culture model that imitates the in vivo cellular context and dynamics of cancer progression, reversion and apoptosis. We will develop algorithms to identify molecular determinants and markers of cancer states and categorize cancers on the basis of signaling pathway characteristics. Using probabilistic graphical modeling approaches, we hope to infer stochastic network models for transcriptional regulation in response to combinations of signaling inhibitions in cancer cells.
Selected Reading:

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Probabilistic evolutionary models of cis-regulatory modules in Drosophila (in collaboration with Martin Kreitman)

In this project we study the evolutionary relationships reflected in the sequence, ordering, position, spacing and function of the regulatory motifs controlling body segmentation during early embryogenesis in multiple species of the Drosophila. We are interested in understanding the biological driving forces, molecular mechanisms and functional implications of motif evolution in general from this biological model, and in developing comparative genomic algorithms for motif finding from unaligned non-coding sequences.

Selected Reading

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Inference of Population Genetic Structure, Variation, Migration, and Evolution Based on Genome Polymorphisms

In this project we develop novel statistical models and computational algorithms based on formalisms such as the coalescent process, Bayesian nonparametrics, admixture models, and various temporal/spatial stochastic processes for uncovering the chromosomal association (i.e., haplotypes), population distribution (i.e., diversity and frequency) inheritance process (i.e., recombination/substitution/selection), and migration history of genetics polymorphisms such as SNPs, to address problems such as ancestry reconstruction, disease-related gene flow, chromosomal evolution and genetic demography in human or organismal populations.

Selected Reading

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Biological sequence analysis: motif detection, gene finding and systems biology

In this project we develop models and algorithms for understanding and uncovering the structure of genomic sequences of higher organisms. We develop Bayesian models for DNA/protein motif detection and gene finding based on both sequence-level signatures and meta-sequence-level structural information reflecting protein-DNA binding, transcript stability, and prior knowledge of the organization rules of regulatory modules. We intend to integrate motif finding with the system biology research of gene regulatory network.

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Last updated 02/1/2009