## Lee, Daniel D

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Publication Room Impulse Response Estimation using Sparse Online Prediction and Absolute Loss(2006-05-24) Crammer, Koby; Lee, Daniel DThe need to accurately and efficiently estimate room impulse responses arises in many acoustic signal processing applications. In this work, we present a general family of algorithms which contain the conventional normalized least mean squares (NLMS) algorithm as a special case. Specific members of this family yield estimates which are robust both to different noise models and choice of parameters. We demonstrate the merits of our approach to accurately estimate sparse room impulse responses in simulations with speech signals.Publication Bayesian Regularization and Nonnegative Deconvolution for Time Delay Estimation(2004-12-13) Lin, Yuanqing; Lee, Daniel DBayesian Regularization and Nonnegative Deconvolution (BRAND) is proposed for estimating time delays of acoustic signals in reverberant environments. Sparsity of the nonnegative filter coefficients is enforced using an L1-norm regularization. A probabilistic generative model is used to simultaneously estimate the regularization parameters and filter coefficients from the signal data. Iterative update rules are derived under a Bayesian framework using the Expectation-Maximization procedure. The resulting time delay estimation algorithm is demonstrated on noisy acoustic data.Publication Nonnegative deconvolution for time of arrival estimation(2004-05-17) Lin, Yuanqing; Lee, Daniel D; Saul, Lawrence KThe interaural time difference (ITD) of arrival is a primary cue for acoustic sound source localization. Traditional estimation techniques for ITD based upon cross-correlation are related to maximum-likelihood estimation of a simple generative model. We generalize the time difference estimation into a deconvolution problem with nonnegativity constraints. The resulting nonnegative least squares optimization can be efficiently solved using a novel iterative algorithm with guaranteed global convergence properties. We illustrate the utility of this algorithm using simulations and experimental results from a robot platform.Publication Learning a Manifold-Constrained Map between Image Sets: Applications to Matching and Pose Estimation(2006-06-01) Ham, Jihun; Ahn, Ikkjin; Lee, Daniel DThis paper proposes a method for matching two sets of images given a small number of training examples by exploiting the underlying structure of the image manifolds. A nonlinear map from one manifold to another is constructed by combining linear maps locally defined on the tangent spaces of the manifolds. This construction imposes strong constraints on the choice of the maps, and makes possible good generalization of correspondences between all of the image sets. This map is flexible enough to approximate an arbitrary diffeomorphism between manifolds and can serve many purposes for applications. The underlying algorithm is a non-iterative efficient procedure whose complexity mainly depends on the number of matched training examples and the dimensionality of the manifold, and not on the number of samples nor on the dimensionality of the images. Several experiments were performed to demonstrate the potential of our method in image analysis and pose estimation. The first example demonstrates how images from a rotating camera can be mapped to the underlying pose manifold. Second, computer generated images from articulating toy figures are matched using the underlying 4 dimensional manifold to generate image-driven animations. Finally, two sets of actual lip images during speech are matched by their appearance manifold. In all these cases, our algorithm is able to obtain reasonable matches between thousands of large-dimensional images, with a minimum of computation.Publication Bayesian L1-Norm Sparse Learning(2006-05-19) Lee, Daniel D; Lin, YuanqingWe propose a Bayesian framework for learning the optimal regularization parameter in the L1-norm penalized least-mean-square (LMS) problem, also known as LASSO [1] or basis pursuit [2]. The setting of the regularization parameter is critical for deriving a correct solution. In most existing methods, the scalar regularization parameter is often determined in a heuristic manner; in contrast, our approach infers the optimal regularization setting under a Bayesian framework. Furthermore, Bayesian inference enables an independent regularization scheme where each coefficient (or weight) is associated with an independent regularization parameter. Simulations illustrate the improvement using our method in discovering sparse structure from noisy data.Publication Grassmann Discriminant Analysis: a Unifying View on Subspace-Based Learning(2008-07-06) Hamm, Jihun; Lee, Daniel DIn this paper we propose a discriminant learning framework for problems in which data consist of linear subspaces instead of vectors. By treating subspaces as basic elements, we can make learning algorithms adapt naturally to the problems with linear invariant structures. We propose a unifying view on the subspace-based learning method by formulating the problems on the Grassmann manifold, which is the set of fixed-dimensional linear subspaces of a Euclidean space. Previous methods on the problem typically adopt an inconsistent strategy: feature extraction is performed in the Euclidean space while non-Euclidean distances are used. In our approach, we treat each subspace as a point in the Grassmann space, and perform feature extraction and classification in the same space. We show feasibility of the approach by using the Grassmann kernel functions such as the Projection kernel and the Binet-Cauchy kernel. Experiments with real image databases show that the proposed method performs well compared with state-of- the-art algorithms.Publication Multiplicative Updates for Large Margin Classifiers(2003-08-24) Saul, Lawrence K; Sha, Fei; Lee, Daniel DVarious problems in nonnegative quadratic programming arise in the training of large margin classifiers. We derive multiplicative updates for these problems that converge monotonically to the desired solutions for hard and soft margin classifiers. The updates differ strikingly in form from other multiplicative updates used in machine learning. In this paper, we provide complete proofs of convergence for these updates and extend previous work to incorporate sum and box constraints in addition to nonnegativity.Publication Relevant Deconvolution For Acoustic Source Estimation(2005-03-18) Lin, Yuanqing; Lee, Daniel DWe describe a robust deconvolution algorithm for simultaneously estimating an acoustic source signal and convolutive filters associated with the acoustic room impulse responses from a pair of microphone signals. In contrast to conventional blind deconvolution techniques which rely upon a knowledge of the statistics of the source signal, our algorithm exploits the nonnegativity and sparsity structure of room impulse responses. The algorithm is formulated as a quadratic optimization problem with respect to both the source signal and filter coefficients, and proceeds by iteratively solving the optimization in two alternating steps. In the H-step, the nonnegative filter coefficients are optimally estimated within a Bayesian framework using a relevant set of regularization parameters. In the S-step, the source signal is estimated without any prior assumption on its statistical distribution. The resulting estimates converge to a relevant solution exhibiting appropriate sparseness in the filters. Simulation results indicate that the algorithm is able to precisely recover both the source signal and filter coefficients, even in the presence of large ambient noise.Publication Multiplicative Updates for Nonnegative Quadratic Programming(2007-01-01) Lin, Yuanqing; Sha, Fei; Lee, Daniel D; Saul, Lawrence K.Many problems in neural computation and statistical learning involve optimizations with nonnegativity constraints. In this article, we study convex problems in quadratic programming where the optimization is confined to an axis-aligned region in the nonnegative orthant. For these problems, we derive multiplicative updates that improve the value of the objective function at each iteration and converge monotonically to the global minimum. The updates have a simple closed form and do not involve any heuristics or free parameters that must be tuned to ensure convergence. Despite their simplicity, they differ strikingly in form from other multiplicative updates used in machine learning.We provide complete proofs of convergence for these updates and describe their application to problems in signal processing and pattern recognition.Publication An Information Maximization Approach to Overcomplete and Recurrent Representations(2000-11-27) Shriki, Oren; Sompolinsky, Haim; Lee, Daniel DThe principle of maximizing mutual information is applied to learning overcomplete and recurrent representations. The underlying model consists of a network of input units driving a larger number of output units with recurrent interactions. In the limit of zero noise, the network is deterministic and the mutual information can be related to the entropy of the output units. Maximizing this entropy with respect to both the feedforward connections as well as the recurrent interactions results in simple learning rules for both sets of parameters. The conventional independent components (ICA) learning algorithm can be recovered as a special case where there is an equal number of output units and no recurrent connections. The application of these new learning rules is illustrated on a simple two-dimensional input example.