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 Statistical Learning


Reviews: Regularized Modal Regression with Applications in Cognitive Impairment Prediction

Neural Information Processing Systems

The authors present a regularized modal regression method. The statistical learning view of this proposed method is studied and the resulting model is applied to Alzheimer's disease studies. There are several presentation and evaluation issues for this work in its current form. Firstly, the authors motivate the paper using Alzheimer's disease studies and argue that modal regression is the way to analyze correlations between several disease markers of the disease. The necessity of use conditional mode for regression has nothing specific for the Alzheimer's application. The motivation for RMR makes sense without any AD related context.


Reviews: Connectionist Temporal Classification with Maximum Entropy Regularization

Neural Information Processing Systems

This work presents a method for end-to-end sequence learning, and more specifically in the framework of Connectionist Temporal Classification (CTC). The paper has two main contributions: - The first is a regularization of the training of the CTC objective in order to reduce the over-confidence of the model. In order to do that, the authors propose a method based on conditional entropy. More specifically, the proposed regularization would encourages the model to explore paths that are close to the dominant one. In order to do so, they suppose that the consecutive elements of a sequence have equal spacing.


Reviews: Using Large Ensembles of Control Variates for Variational Inference

Neural Information Processing Systems

Thank you for the thoughtful response. I have read the other reviews and the rebuttal, and after discussing the work I am electing to keep my score the same. I am somewhat unsatisfied by the author response; for papers where gradient estimator efficiency (in terms of variance) is in service of the optimization problem, comparing ELBO traces by iteration can be very misleading. If the machinery you introduce to efficiently use an ensemble of control variates is not very costly, then it should be measured or shown in your experiments. My comments below weren't about optimal tuning, they were more about exploring/understanding the sensitivity of their method on the parameters they introduce.


Reviews: Speeding Up Latent Variable Gaussian Graphical Model Estimation via Nonconvex Optimization

Neural Information Processing Systems

The paper considers learning the dependency structure of Gaussian graphical models where some variables are latent. Directly applying the usual assumption of sparsity in the precision matrix is difficult because variables that appear correlated might actually both depend on a common latent variable. Previously, Chandrasekaran et al. proposed estimating the model structure by decomposing the full precision matrix into the sum of of a sparse matrix and a low-rank matrix. Likelihood is maximized while the components of the sparse matrix are penalized with an l1 regularizer and the low-rank matrix is penalized with a nuclear norm. Computing the proximal operator to update the low-rank component requires performing SVD in O(d 3) time at each iteration. The authors propose replacing the low-rank component with its Cholesky decomposition ZZ T and finding Z directly.


Reviews: Active Learning for Non-Parametric Regression Using Purely Random Trees

Neural Information Processing Systems

Yet, I still think that their results (including those appearing in their response) are not showing significant gains as seen in other Active Learning settings. The paper addresses the problem of active learning for regression with random trees. The authors introduce a simple'oracle' algorithm and a risk variance is provided for this criterion. Authors provide a risk minimizing query criteria and claim it is better than the random selection criterion An estimation algorithm is presented that provides the necessary statistics at its first stage to allow an approximation to the'oracle' algorithm. Numerical results are presented in which improved performance over random and uncertainty sample is provided for simulated data, and no improvement for real UCI data.


Reviews: Clustering Billions of Reads for DNA Data Storage

Neural Information Processing Systems

The paper presents a solution to a new type of clustering problem that has emerged from studies of DNA-based storage. Information is encoded within DNA sequences and retrieved using short-read sequencing technology. The short-read sequencer will create multiple short overlapping sequence reads and these have to be clustered to establish whether they are from the same place in the original sequence. The characteristics of the clustering problem is that the clusters are pretty tight in terms of edit distance (25 max diameter here - that seems quite broad given current sequencing error rates) but well separated from each other (much larger distance between them than diameter). I thought this was an interesting and timely application.


Reviews: Stochastic Cubic Regularization for Fast Nonconvex Optimization

Neural Information Processing Systems

This submission is interested in stochastic nonconvex optimization problems, in which only stochastic estimates of the objective and its derivatives can be accessed at every iteration. The authors develop a variant of the cubic regularization framework, that only requires access to stochastic gradients and products of stochastic Hessians with vectors. Such a method is shown to reach a point at which the gradient norm is smaller than \epsilon and the minimum Hessian eigenvalue is bigger than -\sqrt{\rho \epsilon} in a number of stochastic queries (gradient or Hessian-vector product) of order of \epsilon {-3.5}, which improves over the classical complexity of Stochastic Gradient Descent (SGD). The problem of interest is clearly introduced, along with the possible advantages of using both stochastic estimates and a cubic regularization framework. The associated literature is correctly reviewed, and the authors even cite contemporary work that achieves similar complexity guarantees but rely on stochastic gradient estimates and variance reduction.


Reviews: Convergence Analysis of Two-layer Neural Networks with ReLU Activation

Neural Information Processing Systems

This paper proves the convergence of a stochastic gradient descent algorithm from a suitable starting point to the global minimizer of a nonconvex energy representing the loss of a two-layer feedforward network with rectified linear unit activation. In particular, the algorithm is shown to converge in two phases, where phase 1 drives the iterates into a one-point convex region which subsequently leads to the actual convergence in phase 2. The findings, the analysis, and particularly the methodology for proving the convergence (in 2 phases) are very interesting and definitely deserve to be published. The entire proof is extremely long (including a flowchart of 15 Lemmas/Theorems that finally allow to show the main theorem in 25 pages of proofs), and I have to admit that I did not check this part. I have some questions on the paper and suggestions to further improve the manuscript: - Figure 1 points out the different structure of the considered networks, and even the abstract already refers to the special structure of "identity mappings". However, optimizing for W (vanilla network) is equivalent to optimizing for (W I), such that the difference seems to lie in different starting points only.


Reviews: K-Medoids For K-Means Seeding

Neural Information Processing Systems

The authors propose to use a particular version of the K-medoids algorithm (clarans - that uses iterative swaps to identify the medoids) for initializing k-means and claim that this improves the final clustering quality. The authors have also tested their claims with multiple datasets, and demonstrated their performance improvements. They have also published code that will be made open after the review process. The paper is easy to read and follow, and the authors have done a good job placing their work in context. I appreciate the fact that the optimizations are presented in a very accessible manner in Section 4. As the authors claim, open source code is an important contribution.


Reviews: Inhomogeneous Hypergraph Clustering with Applications

Neural Information Processing Systems

This paper considers the hypergraph clustering problem in a more general setting where the cost of hyperedge cut depends on the partitioning of hyperedge (i.e., all cuts of the hyperedge are not treated the same). An algorithm is presented for minimizing the normalized cut in this general setting. The algorithm breaks down for general costs of the hyperedge cut; however the authors derive conditions under which the algorithm succeeds and has provable approximation guarantees. Detailed comments: The main contributions of the paper are Generalization of hypergraph partitioning to include inhomogeneous cut of the hyper edge; the motivation for this is clearly established. A novel technique to minimize the normalized cut for this problem.