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Robust Classification Under 𝓁0 Attack for the Gaussian Mixture Model 𝓁0攻击下高斯混合模型的鲁棒分类
Q1 MATHEMATICS, APPLIED Pub Date : 2021-04-05 DOI: 10.1137/21m1426286
Payam Delgosha, Hamed Hassani, Ramtin Pedarsani
It is well-known that machine learning models are vulnerable to small but cleverly-designed adversarial perturbations that can cause misclassification. While there has been major progress in designing attacks and defenses for various adversarial settings, many fundamental and theoretical problems are yet to be resolved. In this paper, we consider classification in the presence of $ell_0$-bounded adversarial perturbations, a.k.a. sparse attacks. This setting is significantly different from other $ell_p$-adversarial settings, with $pgeq 1$, as the $ell_0$-ball is non-convex and highly non-smooth. Under the assumption that data is distributed according to the Gaussian mixture model, our goal is to characterize the optimal robust classifier and the corresponding robust classification error as well as a variety of trade-offs between robustness, accuracy, and the adversary's budget. To this end, we develop a novel classification algorithm called FilTrun that has two main modules: Filtration and Truncation. The key idea of our method is to first filter out the non-robust coordinates of the input and then apply a carefully-designed truncated inner product for classification. By analyzing the performance of FilTrun, we derive an upper bound on the optimal robust classification error. We also find a lower bound by designing a specific adversarial strategy that enables us to derive the corresponding robust classifier and its achieved error. For the case that the covariance matrix of the Gaussian mixtures is diagonal, we show that as the input's dimension gets large, the upper and lower bounds converge; i.e. we characterize the asymptotically-optimal robust classifier. Throughout, we discuss several examples that illustrate interesting behaviors such as the existence of a phase transition for adversary's budget determining whether the effect of adversarial perturbation can be fully neutralized.
众所周知,机器学习模型很容易受到小而巧妙设计的对抗性扰动的影响,这些扰动可能导致错误分类。虽然在设计各种对抗环境的攻击和防御方面取得了重大进展,但许多基本和理论问题尚未得到解决。在本文中,我们考虑在存在的分类 $ell_0$-有界对抗性扰动,又名稀疏攻击。这种设置与其他设置明显不同 $ell_p$-对抗性设置,与 $pgeq 1$,作为… $ell_0$-球是非凸的,高度不光滑。在假设数据按照高斯混合模型分布的情况下,我们的目标是表征最优鲁棒分类器和相应的鲁棒分类误差,以及鲁棒性、准确性和对手预算之间的各种权衡。为此,我们开发了一种新的分类算法FilTrun,它有两个主要模块:过滤和截断。我们的方法的关键思想是首先过滤掉输入的非鲁棒坐标,然后应用精心设计的截断内积进行分类。通过分析FilTrun算法的性能,给出了最优鲁棒分类误差的上界。我们还通过设计一个特定的对抗策略来找到一个下界,该策略使我们能够推导出相应的鲁棒分类器及其实现的误差。对于高斯混合的协方差矩阵为对角线的情况,我们证明了随着输入维数的增大,上下界收敛;即我们描述渐近最优鲁棒分类器。在整个过程中,我们讨论了几个例子,说明有趣的行为,如存在的相位转变的对手的预算决定是否对抗性扰动的影响可以完全抵消。
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引用次数: 5
Nonlinear Weighted Directed Acyclic Graph and A Priori Estimates for Neural Networks 神经网络的非线性加权有向无环图和先验估计
Q1 MATHEMATICS, APPLIED Pub Date : 2021-03-30 DOI: 10.1137/21M140955
Yuqing Li, Tao Luo, Chao Ma
In an attempt to better understand structural benefits and generalization power of deep neural networks, we firstly present a novel graph theoretical formulation of neural network models, including fully connected, residual network (ResNet) and densely connected networks (DenseNet). Secondly, we extend the error analysis of the population risk for two layer network cite{ew2019prioriTwo} and ResNet cite{e2019prioriRes} to DenseNet, and show further that for neural networks satisfying certain mild conditions, similar estimates can be obtained. These estimates are a priori in nature since they depend sorely on the information prior to the training process, in particular, the bounds for the estimation errors are independent of the input dimension.
为了更好地理解深度神经网络的结构优势和泛化能力,我们首先提出了一种新的神经网络模型的图理论公式,包括全连接、残差网络(ResNet)和密集连接网络(DenseNet)。其次,我们将两层网络cite{ew2019prioriTwo}和ResNet cite{e2019prioriRes}的人口风险误差分析扩展到DenseNet,进一步证明对于满足一定温和条件的神经网络,可以得到类似的估计。这些估计本质上是先验的,因为它们完全依赖于训练过程之前的信息,特别是,估计误差的界限与输入维度无关。
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引用次数: 0
Fast Cluster Detection in Networks by First Order Optimization 基于一阶优化的网络快速聚类检测
Q1 MATHEMATICS, APPLIED Pub Date : 2021-03-29 DOI: 10.1137/21m1408658
I. Bomze, F. Rinaldi, Damiano Zeffiro
Cluster detection plays a fundamental role in the analysis of data. In this paper, we focus on the use of s-defective clique models for network-based cluster detection and propose a nonlinear optimization approach that efficiently handles those models in practice. In particular, we introduce an equivalent continuous formulation for the problem under analysis, and we analyze some tailored variants of the Frank-Wolfe algorithm that enable us to quickly find maximal s-defective cliques. The good practical behavior of those algorithmic tools, which is closely connected to their support identification properties, makes them very appealing in practical applications. The reported numerical results clearly show the effectiveness of the proposed approach.
聚类检测在数据分析中起着重要的作用。在本文中,我们着重于使用s缺陷团模型进行基于网络的聚类检测,并提出了一种在实践中有效处理这些模型的非线性优化方法。特别地,我们为所分析的问题引入了一个等效连续公式,并分析了Frank-Wolfe算法的一些定制变体,使我们能够快速找到最大的s缺陷团。这些算法工具具有良好的实用性能,这与它们的支持识别特性密切相关,这使得它们在实际应用中非常有吸引力。所报道的数值结果清楚地表明了所提出方法的有效性。
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引用次数: 6
Quantitative approximation results for complex-valued neural networks 复值神经网络的定量逼近结果
Q1 MATHEMATICS, APPLIED Pub Date : 2021-02-25 DOI: 10.1137/21m1429540
A. Caragea, D. Lee, J. Maly, G. Pfander, F. Voigtlaender
Until recently, applications of neural networks in machine learning have almost exclusively relied on real-valued networks. It was recently observed, however, that complex-valued neural networks (CVNNs) exhibit superior performance in applications in which the input is naturally complex-valued, such as MRI fingerprinting. While the mathematical theory of real-valued networks has, by now, reached some level of maturity, this is far from true for complex-valued networks. In this paper, we analyze the expressivity of complex-valued networks by providing explicit quantitative error bounds for approximating $C^n$ functions on compact subsets of $mathbb{C}^d$ by complex-valued neural networks that employ the modReLU activation function, given by $sigma(z) = mathrm{ReLU}(|z| - 1) , mathrm{sgn} (z)$, which is one of the most popular complex activation functions used in practice. We show that the derived approximation rates are optimal (up to log factors) in the class of modReLU networks with weights of moderate growth.
直到最近,神经网络在机器学习中的应用几乎完全依赖于实值网络。然而,最近观察到,复杂值神经网络(cvnn)在输入自然是复杂值的应用中表现出优异的性能,例如MRI指纹识别。虽然到目前为止,实值网络的数学理论已经达到了一定的成熟程度,但对于复值网络来说,这还远远不够。本文通过给出复值神经网络在$mathbb{C}^d$的紧子集上逼近$C^n$函数的显式定量误差界,分析了复值网络的可表达性。该复值神经网络使用的modReLU激活函数由$sigma(z) = mathm {ReLU}(|z| - 1) , mathm {sgn} (z)$给出,这是实践中最常用的复激活函数之一。我们表明,在权重适度增长的modReLU网络类中,导出的近似率是最优的(高达对数因子)。
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引用次数: 4
Approximation Bounds for Sparse Programs 稀疏规划的近似界
Q1 MATHEMATICS, APPLIED Pub Date : 2021-02-12 DOI: 10.1137/21m1398677
Armin Askari, A. d’Aspremont, L. Ghaoui
We show that sparsity constrained optimization problems over low dimensional spaces tend to have a small duality gap. We use the Shapley-Folkman theorem to derive both data-driven bounds on the duality gap, and an efficient primalization procedure to recover feasible points satisfying these bounds. These error bounds are proportional to the rate of growth of the objective with the target cardinality, which means in particular that the relaxation is nearly tight as soon as the target cardinality is large enough so that only uninformative features are added.
我们证明了低维空间上的稀疏约束优化问题往往具有较小的对偶间隙。我们利用Shapley-Folkman定理推导了对偶间隙上的数据驱动边界,并给出了一个有效的初始化过程来恢复满足这些边界的可行点。这些误差界限与目标基数的增长速度成正比,这特别意味着,一旦目标基数足够大,松弛几乎是紧密的,因此只添加了无信息的特征。
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引用次数: 2
A Variational Formulation of Accelerated Optimization on Riemannian Manifolds 黎曼流形加速优化的变分公式
Q1 MATHEMATICS, APPLIED Pub Date : 2021-01-16 DOI: 10.1137/21m1395648
Valentin Duruisseaux, M. Leok
It was shown recently by Su et al. (2016) that Nesterov's accelerated gradient method for minimizing a smooth convex function $f$ can be thought of as the time discretization of a second-order ODE, and that $f(x(t))$ converges to its optimal value at a rate of $mathcal{O}(1/t^2)$ along any trajectory $x(t)$ of this ODE. A variational formulation was introduced in Wibisono et al. (2016) which allowed for accelerated convergence at a rate of $mathcal{O}(1/t^p)$, for arbitrary $p>0$, in normed vector spaces. This framework was exploited in Duruisseaux et al. (2021) to design efficient explicit algorithms for symplectic accelerated optimization. In Alimisis et al. (2020), a second-order ODE was proposed as the continuous-time limit of a Riemannian accelerated algorithm, and it was shown that the objective function $f(x(t))$ converges to its optimal value at a rate of $mathcal{O}(1/t^2)$ along solutions of this ODE. In this paper, we show that on Riemannian manifolds, the convergence rate of $f(x(t))$ to its optimal value can also be accelerated to an arbitrary convergence rate $mathcal{O}(1/t^p)$, by considering a family of time-dependent Bregman Lagrangian and Hamiltonian systems on Riemannian manifolds. This generalizes the results of Wibisono et al. (2016) to Riemannian manifolds and also provides a variational framework for accelerated optimization on Riemannian manifolds. An approach based on the time-invariance property of the family of Bregman Lagrangians and Hamiltonians was used to construct very efficient optimization algorithms in Duruisseaux et al. (2021), and we establish a similar time-invariance property in the Riemannian setting. One expects that a geometric numerical integrator that is time-adaptive, symplectic, and Riemannian manifold preserving will yield a class of promising optimization algorithms on manifolds.
Su et al.(2016)最近表明,用于最小化光滑凸函数$f$的Nesterov加速梯度方法可以被认为是二阶ODE的时间离散化,并且$f(x(t))$沿着该ODE的任何轨迹$x(t)$以$mathcal{O}(1/t^2)$的速率收敛到其最优值。Wibisono等人(2016)引入了一个变分公式,该公式允许在赋范向量空间中以$mathcal{O}(1/t^p)$的速率加速收敛,对于任意$p>0$。Duruisseaux等人(2021)利用该框架为辛加速优化设计了高效的显式算法。在Alimisis et al.(2020)中,提出了二阶ODE作为黎曼加速算法的连续时间极限,并证明了目标函数f(x(t))$沿该ODE的解以$mathcal{O}(1/t^2)$的速率收敛到其最优值。在黎曼流形上,通过考虑黎曼流形上的一类时变布雷格曼-拉格朗日系统和哈密顿系统,我们证明了f(x(t))$到其最优值的收敛速率也可以加速到任意收敛速率$mathcal{O}(1/t^p)$。这将Wibisono等人(2016)的结果推广到黎曼流形,并为黎曼流形的加速优化提供了变分框架。Duruisseaux等人(2021)利用布雷格曼-拉格朗日算子和哈密顿算子族的时不变性质构建了非常高效的优化算法,我们在黎曼设置中建立了类似的时不变性质。人们期望一个具有时间适应性、辛性和保持黎曼流形的几何数值积分器将产生一类有前途的流形优化算法。
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引用次数: 18
Identifying 3D Genome Organization in Diploid Organisms via Euclidean Distance Geometry 通过欧几里得距离几何识别二倍体生物的三维基因组组织
Q1 MATHEMATICS, APPLIED Pub Date : 2021-01-13 DOI: 10.1137/21m1390372
A. Belyaeva, Kaie Kubjas, Lawrence Sun, Caroline Uhler
The spatial organization of the DNA in the cell nucleus plays an important role for gene regulation, DNA replication, and genomic integrity. Through the development of chromosome conformation capture experiments (such as 3C, 4C, Hi-C) it is now possible to obtain the contact frequencies of the DNA at the whole-genome level. In this paper, we study the problem of reconstructing the 3D organization of the genome from such whole-genome contact frequencies. A standard approach is to transform the contact frequencies into noisy distance measurements and then apply semidefinite programming (SDP) formulations to obtain the 3D configuration. However, neglected in such reconstructions is the fact that most eukaryotes including humans are diploid and therefore contain two copies of each genomic locus. We prove that the 3D organization of the DNA is not identifiable from distance measurements derived from contact frequencies in diploid organisms. In fact, there are infinitely many solutions even in the noise-free setting. We then discuss various additional biologically relevant and experimentally measurable constraints (including distances between neighboring genomic loci and higher-order interactions) and prove identifiability under these conditions. Furthermore, we provide SDP formulations for computing the 3D embedding of the DNA with these additional constraints and show that we can recover the true 3D embedding with high accuracy from both noiseless and noisy measurements. Finally, we apply our algorithm to real pairwise and higher-order contact frequency data and show that we can recover known genome organization patterns.
细胞核内DNA的空间组织对基因调控、DNA复制和基因组完整性起着重要作用。通过染色体构象捕获实验(如3C, 4C, Hi-C)的发展,现在可以在全基因组水平上获得DNA的接触频率。在本文中,我们研究了从这些全基因组接触频率重建基因组三维组织的问题。一种标准的方法是将接触频率转换为噪声距离测量值,然后应用半定规划(SDP)公式获得三维构型。然而,在这种重建中被忽视的事实是,大多数真核生物包括人类是二倍体,因此每个基因组位点包含两个拷贝。我们证明,DNA的三维组织是不可识别的距离测量从接触频率在二倍体生物。事实上,即使在无噪声的情况下,也有无限多种解决方案。然后,我们讨论了各种额外的生物学相关和实验可测量的限制(包括邻近基因组位点之间的距离和高阶相互作用),并证明了在这些条件下的可识别性。此外,我们提供了用于计算具有这些附加约束的DNA 3D嵌入的SDP公式,并表明我们可以从无噪声和有噪声测量中以高精度恢复真正的3D嵌入。最后,我们将该算法应用于实际的成对和高阶接触频率数据,并表明我们可以恢复已知的基因组组织模式。
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引用次数: 6
The Convex Mixture Distribution: Granger Causality for Categorical Time Series. 凸混合分布:范畴时间序列的Granger因果关系。
Q1 MATHEMATICS, APPLIED Pub Date : 2021-01-01 DOI: 10.1137/20m133097x
Alex Tank, Xiudi Li, Emily B Fox, Ali Shojaie

We present a framework for learning Granger causality networks for multivariate categorical time series based on the mixture transition distribution (MTD) model. Traditionally, MTD is plagued by a nonconvex objective, non-identifiability, and presence of local optima. To circumvent these problems, we recast inference in the MTD as a convex problem. The new formulation facilitates the application of MTD to high-dimensional multivariate time series. As a baseline, we also formulate a multi-output logistic autoregressive model (mLTD), which while a straightforward extension of autoregressive Bernoulli generalized linear models, has not been previously applied to the analysis of multivariate categorial time series. We establish identifiability conditions of the MTD model and compare them to those for mLTD. We further devise novel and efficient optimization algorithms for MTD based on our proposed convex formulation, and compare the MTD and mLTD in both simulated and real data experiments. Finally, we establish consistency of the convex MTD in high dimensions. Our approach simultaneously provides a comparison of methods for network inference in categorical time series and opens the door to modern, regularized inference with the MTD model.

我们提出了一个基于混合转移分布(MTD)模型的多变量分类时间序列的Granger因果关系网络学习框架。传统上,MTD受到非凸目标、不可识别性和局部最优存在的困扰。为了避免这些问题,我们将MTD中的推理重新定义为凸问题。新的公式促进了MTD在高维多变量时间序列中的应用。作为基线,我们还建立了一个多输出逻辑自回归模型(mLTD),它虽然是自回归伯努利广义线性模型的直接扩展,但以前从未应用于多变量分类时间序列的分析。我们建立了MTD模型的可识别性条件,并将其与mLTD的条件进行了比较。基于我们提出的凸公式,我们进一步设计了新的有效的MTD优化算法,并在模拟和实际数据实验中比较了MTD和mLTD。最后,我们建立了高维凸MTD的一致性。我们的方法同时提供了分类时间序列中网络推理方法的比较,并为MTD模型的现代正则化推理打开了大门。
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引用次数: 0
On the Effectiveness of Richardson Extrapolation in Data Science 论Richardson外推法在数据科学中的有效性
Q1 MATHEMATICS, APPLIED Pub Date : 2021-01-01 DOI: 10.1137/21m1397349
Francis R. Bach
,
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引用次数: 6
Interpretable Approximation of High-Dimensional Data 高维数据的可解释近似
Q1 MATHEMATICS, APPLIED Pub Date : 2021-01-01 DOI: 10.1137/21M1407707
D. Potts, Michael Schmischke
In this paper we apply the previously introduced approximation method based on the ANOVA (analysis of variance) decomposition and Grouped Transformations to synthetic and real data. The advantage of this method is the interpretability of the approximation, i.e., the ability to rank the importance of the attribute interactions or the variable couplings. Moreover, we are able to generate an attribute ranking to identify unimportant variables and reduce the dimensionality of the problem. We compare the method to other approaches on publicly available benchmark datasets.
本文将基于方差分析(ANOVA)分解和分组变换的逼近方法应用于合成数据和实际数据。这种方法的优点是近似的可解释性,即能够对属性相互作用或变量耦合的重要性进行排序。此外,我们能够生成一个属性排序来识别不重要的变量并降低问题的维度。我们将该方法与公开可用的基准数据集上的其他方法进行比较。
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引用次数: 12
期刊
SIAM journal on mathematics of data science
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