Most existing image denoising approaches assumed the noise to be homogeneous white Gaussian distributed with known intensity. However, in real noisy images, the noise models are usually unknown beforehand and can be much more complex. This paper addresses this problem and proposes a novel blind image denoising algorithm to recover the clean image from noisy one with the unknown noise model. To model the empirical noise of an image, our method introduces the mixture of Gaussian distribution, which is flexible enough to approximate different continuous distributions. The problem of blind image denoising is reformulated as a learning problem. The procedure is to first build a two-layer structural model for noisy patches and consider the clean ones as latent variable. To control the complexity of the noisy patch model, this work proposes a novel Bayesian nonparametric prior called "Dependent Dirichlet Process Tree" to build the model. Then, this study derives a variational inference algorithm to estimate model parameters and recover clean patches. We apply our method on synthesis and real noisy images with different noise models. Comparing with previous approaches, ours achieves better performance. The experimental results indicate the efficiency of the proposed algorithm to cope with practical image denoising tasks.

A generalized linear model (GLM) is a flexible extension of linear regression which allows the response or the output to be a nonlinear function of the input via an activation function. In other words, in a GLM, the linear regression of the input is passed through an activation function to generate the response. GLMs unify popular frameworks such as logistic regression and Poisson regression with linear regression. At the same time, they can be learnt with guarantees using simple iterative methods (Kakade et al., 2011). In many scenarios, however, GLMs may be too simplistic, and mixtures of GLMs can be much more effective since they combine the expressive power of latent variables with the predictive capabilities of the GLM. Mixtures of GLMs have widespread applicability including object recognition (Quattoni et al., 2004), human action recognition (Wang and Mori, 2009), syntactic parsing (Petrov and Klein, 2007), and machine translation (Liang et al., 2006). Traditionally, mixture models are learnt through heuristics such as expectation maximization (EM) (Jordan and Jacobs, 1994; Xu et al., 1995) or variational Bayes (Bishop and Svensen, 2003). However, these methods can converge to spurious local optima and have slow convergence rates for high dimensional models. In contrast, we employ a method-of-moments approach for guaranteed learning of mixtures of GLMs.

Recommender systems (RSs) provide an effective way of alleviating the information overload problem by selecting personalized choices. Online social networks and user-generated content provide diverse sources for recommendation beyond ratings, which present opportunities as well as challenges for traditional RSs. Although social matrix factorization (Social MF) can integrate ratings with social relations and topic matrix factorization can integrate ratings with item reviews, both of them ignore some useful information. In this paper, we investigate the effective data fusion by combining the two approaches, in two steps. First, we extend Social MF to exploit the graph structure of neighbors. Second, we propose a novel framework MR3 to jointly model these three types of information effectively for rating prediction by aligning latent factors and hidden topics. We achieve more accurate rating prediction on two real-life datasets. Furthermore, we measure the contribution of each data source to the proposed framework.

In this paper we present a connection between two dynamical systems arising in entirely different contexts: one in signal processing and the other in biology. The first is the famous Iteratively Reweighted Least Squares (IRLS) algorithm used in compressed sensing and sparse recovery while the second is the dynamics of a slime mold (Physarum polycephalum). Both of these dynamics are geared towards finding a minimum l1-norm solution in an affine subspace. Despite its simplicity the convergence of the IRLS method has been shown only for a certain regularization of it and remains an important open problem. Our first result shows that the two dynamics are projections of the same dynamical system in higher dimensions. As a consequence, and building on the recent work on Physarum dynamics, we are able to prove convergence and obtain complexity bounds for a damped version of the IRLS algorithm.

Streaming variational Bayes (SVB) is successful in learning LDA models in an online manner. However previous attempts toward developing online Monte-Carlo methods for LDA have little success, often by having much worse perplexity than their batch counterparts. We present a streaming Gibbs sampling (SGS) method, an online extension of the collapsed Gibbs sampling (CGS). Our empirical study shows that SGS can reach similar perplexity as CGS, much better than SVB. Our distributed version of SGS, DSGS, is much more scalable than SVB mainly because the updates' communication complexity is small.

We consider the problem of learning user preferences over robot trajectories for environments rich in objects and humans. This is challenging because the criterion defining a good trajectory varies with users, tasks and interactions in the environment. We represent trajectory preferences using a cost function that the robot learns and uses it to generate good trajectories in new environments. We design a crowdsourcing system - PlanIt, where non-expert users label segments of the robot's trajectory. PlanIt allows us to collect a large amount of user feedback, and using the weak and noisy labels from PlanIt we learn the parameters of our model. We test our approach on 122 different environments for robotic navigation and manipulation tasks. Our extensive experiments show that the learned cost function generates preferred trajectories in human environments. Our crowdsourcing system is publicly available for the visualization of the learned costs and for providing preference feedback: \url{http://planit.cs.cornell.edu}

The community detection problem refers to finding the underlying communities within a network using only the knowledge of the network topology [16, 31]. This paper considers the following probabilistic model for generating a network with underlying community structures: Suppose that out of a total of n vertices, rK of them are partitioned into r clusters of size K, and the remaining n rK vertices do not belong to any clusters (called outlier vertices); a random graph G is generated based on the cluster structure, where each pair of vertices is connected independently with probability p if they are in the same cluster or q otherwise. In particular, an outlier vertex is connected to any other vertex with probability q. This random graph ensemble is known as the planted cluster model [10] with parameters n, r, K N and p, q [0, 1] such that n rK. In particular, we call p and q the in-cluster and cross-cluster edge density, respectively. The planted cluster model encompasses several classical planted random graph models including planted clique [5], planted coloring [4], planted dense subgraph [6], planted partition [11], and the stochastic block model [23], which have been widely used for studying the community detection and graph partitioning problem (see, e.g., [26, 12, 30, 9] and the references therein). This paper was accepted to IEEE Transactions on Information Theory on January 3, 2016. The material in this paper was presented in part at the IEEE International Symposium on Information Theory, Hong Kong, June, 2015 [20].

Max-product Belief Propagation (BP) is a popular message-passing algorithm for computing a Maximum-A-Posteriori (MAP) assignment over a distribution represented by a Graphical Model (GM). It has been shown that BP can solve a number of combinatorial optimization problems including minimum weight matching, shortest path, network flow and vertex cover under the following common assumption: the respective Linear Programming (LP) relaxation is tight, i.e., no integrality gap is present. However, when LP shows an integrality gap, no model has been known which can be solved systematically via sequential applications of BP. In this paper, we develop the first such algorithm, coined Blossom-BP, for solving the minimum weight matching problem over arbitrary graphs. Each step of the sequential algorithm requires applying BP over a modified graph constructed by contractions and expansions of blossoms, i.e., odd sets of vertices. Our scheme guarantees termination in O(n^2) of BP runs, where n is the number of vertices in the original graph. In essence, the Blossom-BP offers a distributed version of the celebrated Edmonds' Blossom algorithm by jumping at once over many sub-steps with a single BP. Moreover, our result provides an interpretation of the Edmonds' algorithm as a sequence of LPs.

This page includes forthcoming AAAI sponsored conferences, conferences presented by AAAI Affiliates, and conferences held in cooperation with AAAI. AI Magazine also maintains a calendar listing that includes nonaffiliated conferences at www.aaai.org/Magazine/calendar.php. AAAI-16 will be held Principles of Knowledge Representation on Semantic Computing. ICSC will February 12-17, 2016 in Phoenix, Arizona and Reasoning (KR 2016) be held February 3-5, 2016, in Laguna USA. Twenty-Ninth International Florida on Biomedical Engineering Systems IAAI-16 will be held will be AI Research Society Conference. and Technologies.

For the vast majority of queries (for example, navigation, simple fact lookup, and others), search engines do extremely well. Their ability to quickly provide answers to queries is a remarkable testament to the power of many of the fundamental methods of AI. They also highlight many of the issues that are common to sophisticated AI question-answering systems. It has become clear that people think of search programs in ways that are very different from traditional information sources. Rapid and ready-at-hand access, depth of processing, and the way they enable people to offload some ordinary memory tasks suggest that search engines have become more of a cognitive amplifier than a simple repository or front-end to the Internet. Like all sophisticated tools, people still need to learn how to use them. Although search engines are superb at finding and presenting information—up to and including extracting complex relations and making simple inferences—knowing how to frame questions and evaluate their results for accuracy and credibility remains an ongoing challenge. Some questions are still deep and complex, and still require knowledge on the part of the search user to work through to a successful answer. And the fact that the underlying information content, user interfaces, and capabilities are all in a continual state of change means that searchers need to continually update their knowledge of what these programs can (and cannot) do.