nips nips2012 nips2012-317 knowledge-graph by maker-knowledge-mining

317 nips-2012-Smooth-projected Neighborhood Pursuit for High-dimensional Nonparanormal Graph Estimation


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Author: Tuo Zhao, Kathryn Roeder, Han Liu

Abstract: We introduce a new learning algorithm, named smooth-projected neighborhood pursuit, for estimating high dimensional undirected graphs. In particularly, we focus on the nonparanormal graphical model and provide theoretical guarantees for graph estimation consistency. In addition to new computational and theoretical analysis, we also provide an alternative view to analyze the tradeoff between computational efficiency and statistical error under a smoothing optimization framework. Numerical results on both synthetic and real datasets are provided to support our theory. 1

Reference: text


Summary: the most important sentenses genereted by tfidf model

sentIndex sentText sentNum sentScore

1 In particularly, we focus on the nonparanormal graphical model and provide theoretical guarantees for graph estimation consistency. [sent-2, score-0.739]

2 In addition to new computational and theoretical analysis, we also provide an alternative view to analyze the tradeoff between computational efficiency and statistical error under a smoothing optimization framework. [sent-3, score-0.202]

3 1 Introduction We consider the undirected graph estimation problem for a d-dimensional random vector X = (X1 , . [sent-5, score-0.213]

4 Most existing methods for high dimensional graph estimation assume that the random vector X follows a Gaussian distribution, i. [sent-16, score-0.213]

5 Under this parametric assumption, the graph estimation problem can be solved by estimating the sparsity pattern of the precision matrix Ω = Σ−1 , i. [sent-19, score-0.203]

6 There are two major approaches for learning high dimensional Gaussian graphical models: (i) graphical lasso (Yuan and Lin, 2007; Friedman et al. [sent-23, score-0.335]

7 , 2008) and (ii) neighborhood pursuit (Meinshausen and B¨ hlmann, 2006). [sent-25, score-0.572]

8 The graphical lasso maximizes the 1 -penalized Gaussian likelihood and u simultaneously estimates the precision matrix Ω and graph G. [sent-26, score-0.259]

9 In contrast, the neighborhood pursuit method maximizes the 1 -penalized pseudo-likelihood and can only estimate the graph G. [sent-27, score-0.696]

10 Theoretically, both methods are consistent in graph recovery for Gaussian models under certain regularity conditions. [sent-31, score-0.161]

11 (2011) suspect that the neighborhood pursuit approach has a better sample complexity in graph recovery than the graphical lasso. [sent-33, score-0.82]

12 (2009), an semiparametric nonparanormal model is proposed to relax the restrictive normality assumption. [sent-36, score-0.563]

13 (2009) show that for the nonparanormal distribution, the graph G can also be estimated by examining the sparsity pattern of Ω. [sent-44, score-0.637]

14 Different methods have been proposed to infer the nonparanormal model in high dimensions. [sent-45, score-0.481]

15 (2012), a rank-based estimator named nonparanormal SKEPTIC is proposed to directly estimate Ω. [sent-47, score-0.6]

16 Their main idea is to calculate a rank-correlation matrix (either based on the Spearman’s rho or Kendall’s tau correlation) and plug the estimated correlation matrix into the graphical lasso to estimate Ω and graph G. [sent-48, score-0.466]

17 Such a procedure has been proven to be robust and achieve the same parametric rates of convergence as the graphical lasso (Liu et al. [sent-49, score-0.206]

18 However, how to combine the nonparanormal SKEPTIC estimator with the neighborhood pursuit approach is still an open problem. [sent-51, score-1.138]

19 In this paper, we bridge this gap by proposing a novel smooth-projected neighborhood pursuit method. [sent-54, score-0.572]

20 The main idea is to project the possibly indefinite nonparanormal SKEPTIC correlation matrix estimator into the cone of all positive semi-definite matrices with respect to a smoothed elementwise ∞ -norm. [sent-55, score-0.837]

21 Such a projection step is closely related to the dual smoothing approach in Nesterov (2005). [sent-56, score-0.157]

22 Computationally, our proposed smoothed elementwise ∞ -norm has nice structure so that we can √ develop an efficient fast proximal gradient solver with a provable convergence rate O(1/ ) ( is the desired accuracy of the objective value, Nesterov (1988)). [sent-58, score-0.351]

23 Theoretically, we provide sufficient conditions to guarantee that the proposed smooth-projected neighborhood pursuit approach is graph estimation consistent. [sent-59, score-0.769]

24 In addition to new computational and statistical analysis, we further provide an alternative view to analyze the fundamental tradeoff between computational efficiency and statistical error under the smoothing optimization framework. [sent-60, score-0.232]

25 , 2012) considers the dual smoothing approach as a tradeoff between computational efficiency and approximation error. [sent-62, score-0.144]

26 However, we directly consider the statistical error introduced by the smoothing approach, and show that the obtained estimator preserves the good statistical properties without losing the computational efficiency. [sent-65, score-0.314]

27 The rest of this paper is organized as follows: The next section reviews the nonparanormal SKEPTIC in Liu et al. [sent-67, score-0.552]

28 (2012); Section 3 introduces the smooth-projected neighborhood pursuit and derives the fast proximal gradient algorithm; Section 4 explores the statistical properties of the procedure; Section 5 and 6 present results on on both simulated and real datasets. [sent-68, score-0.713]

29 , vd )T ∈ Rd , we define the vector norms: 2 2 d×d ||v||1 = and j vj , and ||v||∞ = maxj |vi |. [sent-77, score-0.151]

30 Let A = [Ajk ] ∈ R j |vj |, ||v||2 = B = [Bjk ] ∈ Rd×d be two symmetric matrices, we define the matrix operator norms: ||A||1 = maxk j |Ajk |, ||A||∞ = maxj k |Ajk |, ||A||2 = max||v||2 =1 ||Av||2 and elementwise norms |||A|||1 = j,k |Ajk |, |||A|||∞ = maxj,k |Ajk |, ||A||2 = j,k |Ajk |2 . [sent-78, score-0.166]

31 The nonparanormal (nonparametric normal) distribution was initially motivated by the sparse additive models (Ravikumar et al. [sent-91, score-0.552]

32 , fd } be a collection of non-decreasing univariate functions and Σ∗ ∈ Rd×d be a correlation matrix with diag(Σ∗ ) = 1. [sent-100, score-0.096]

33 , Xd )T follows a nonparanormal distribution, denoted by X ∼ N P Nd (f, Σ∗ ), if f (X) = (f1 (X1 ), . [sent-104, score-0.481]

34 1) The nonparanormal family is equivalent to the Gaussian copula family for continuous distributions (Klaassen and Wellner, 1997; Tsukahara, 2005; Liu et al. [sent-109, score-0.61]

35 Similar to the Gaussian graphical model, the nonparanormal graphical model also encodes the conditional independence graph by the sparsity pattern of the precision matrix Ω∗ = (Σ∗ )−1 . [sent-111, score-0.811]

36 (2012) propose a rank-based procedure, named nonparanormal SKEPTIC, for learning nonparanromal graphical models. [sent-115, score-0.602]

37 , xi )T 1 d be n independent observations of X, we define the Spearman’s rho and Kendall’s tau correlation coefficients as n i i ¯ ¯ i=1 (rj − rj )(rk − rk ) Spearman’s rho : ρjk = , (2. [sent-122, score-0.308]

38 2) n n i i ¯ 2 ¯ 2 i=1 (rj − rj ) · i=1 (rk − rk ) Kendall’s tau : τjk = 2 n(n − 1) sign xi − xi j j xi − xi , k k (2. [sent-123, score-0.16]

39 The smoothed elementwise ∞ -norm is a smooth convex function. [sent-136, score-0.174]

40 7) S we can also obtain a good correlation estimator without losing computational efficiency. [sent-144, score-0.225]

41 7) has a minimum eigenvalue constraint, regarding which, we exploit Nesterov (1988) and derive the following fast proximal gradient algorithm. [sent-147, score-0.111]

42 The main idea is to utilize the gradients in previous iterations to help find the descent direction for the current iteration, and eventually achieves a faster convergence rate than the ordinary projected gradient algorithm. [sent-148, score-0.102]

43 Suppose A has the eigenvalue decomposition as A = j=1 σj vj vj , where σj ’s are the eigenvalues and vj ’s are corresponding eigenvectors. [sent-160, score-0.279]

44 2, the fast proximal gradient algorithm takes Q(W, W(t−1) , µ) = |||S − W(t−1) |||µ + G(t) , W − W(t−1) + ∞ W(t) = argmin Q(W, W(t−1) , µ) = Π+ W(t−1) − W 0 µ (t) G , θt (3. [sent-174, score-0.111]

45 14) The detailed proof can be found in the extended draft Zhao et al. [sent-182, score-0.112]

46 In next section, by directly analyzing the tradeoff between the computational efficiency and statistical error, we will show that choosing a suitable smooth parameter µ allows S concentrate to Σ∗ with a rate similar to Lemma 2. [sent-187, score-0.157]

47 Due to space limit, all the proofs of following theorems can be found in the extended draft Zhao et al. [sent-192, score-0.112]

48 The next theorem establishes the concentration property of S under the elementwise ∞ norm. [sent-194, score-0.11]

49 Given the nonparanormal SKEPTIC estimator S, for any large enough n, under the conditions that µ ≤ 4πϕ and ϕ > 0, we have the optimum to (3. [sent-198, score-0.592]

50 It implies that we can gain the computational efficiency without losing statistical rate in terms of elementwise sup-norm as long as µ is reasonably large. [sent-203, score-0.292]

51 We now show that our proposed smooth-projected neighborhood approach recovers the true neighborhood for each node with high probability under the following irrepresentable condition (Zhao and Yu, 2006; Zou, 2006; Wainwright, 2009). [sent-204, score-0.515]

52 Recall that Ij and Jj denote the true neighborhood and non-neighborhood of node j respectively. [sent-206, score-0.24]

53 3) The proposed projection approach can be also combined with other graph estimation method such as Zhou et al. [sent-214, score-0.316]

54 It guarantees that for each individual node, we can correctly recover its neighborhood with high probability. [sent-227, score-0.24]

55 Consequently, the following corollary can be implied so that we can asymptotically recover the underlying graph structure under given conditions. [sent-228, score-0.124]

56 (2012) recommend to use the Kendall’s tau for nonparanormal graph estimation because of its superior robustness property compared to the Spearman’s rho. [sent-237, score-0.733]

57 In this section, we use the Kendall’s tau in our smooth-projected neighborhood pursuit method. [sent-238, score-0.653]

58 We adopt the power function g(t) = sign(t)|t|4 to convert the Gaussian data to the nonparanormal data. [sent-241, score-0.481]

59 We use the ROC curve to evaluate the graph estimation performance. [sent-244, score-0.171]

60 Since d > n, the full solution paths cannot be obtained, therefore we restrict the range of false positive edge discovery rates to be from 0 to 0. [sent-245, score-0.119]

61 Nonparanormal SKEPTIC Estimator We first evaluate the proposed smoothed elementwise ∞ -norm projection algorithm. [sent-249, score-0.248]

62 We study the empirical performance of the proposed fast proximal gradient algorithm using different smoothing parameters (µ = 1, 0. [sent-251, score-0.194]

63 The optimization and statistical error curves for different smoothing parameters (averaged over 50 replications) are presented in Figure 1. [sent-255, score-0.147]

64 We further compare the graph recovery performance of our proposed method with the naive indefinite nonparanormal SKEPTIC estimator as in Liu et al. [sent-265, score-0.894]

65 The averaged ROC curves over 100 replications are presented in Figure 2. [sent-267, score-0.115]

66 We see that directly plugging the indefinite nonparanormal SKEPTIC estimator into the neighborhood pursuit results in the worst performance. [sent-268, score-1.138]

67 0 our smoothed-projected neighborhood pursuit method significantly outperforms the naive indefinite nonparanormal SKEPTIC estimator. [sent-327, score-1.149]

68 4 False Positive Rate (c) Chain (d) Scale-free Figure 2: The averaged ROC curves of the neighborhood pursuit when combined with different correlation estimators. [sent-336, score-0.684]

69 “SKEPTIC” represents the indefinite nonparanormal SKEPTIC estimator, and “Projection” represents our proposed projection approach. [sent-337, score-0.555]

70 (2012) to compare our proposed method with the naive neighborhood pursuit method. [sent-386, score-0.668]

71 The naive neighborhood pursuit directly exploits the Pearson correlation estimator under the neighborhood pursuit framework. [sent-387, score-1.379]

72 The averaged ROC curves over 100 replications are presented in Figure 3. [sent-389, score-0.115]

73 As can be seen, our proposed projection method outperforms the naive neighborhood pursuit throughout all four different graphs. [sent-390, score-0.742]

74 30 False Positive Rate (d) Scale-free Figure 3: The averaged ROC curves of the neighborhood pursuit when combined with different correlation estimators. [sent-398, score-0.684]

75 6 Real Data Analysis In this section we present a real data experiment to compare the nonparanormal graphical model to Gaussian graphical model. [sent-401, score-0.655]

76 For model selection, we use the stability graph procedure (Meinshausen 7 and B¨ hlmann, 2010; Liu et al. [sent-402, score-0.222]

77 The topic graph is first used in Blei and Lafferty (2007) to illustrate the idea of correlated topic modeling. [sent-404, score-0.286]

78 Blei and Lafferty (2007) assume that the topic proportion approximately follows a normal distribution after the logarithmic-transformation. [sent-407, score-0.108]

79 Here we are interested in visualizing the relationship among the topics using an undirected graph: the nodes represent individual topics, and edges connecting different nodes represent highly related topics. [sent-408, score-0.151]

80 Evaluated by the Kolmogorov-Smirnov test, we find many topic data highly violate the normality assumption (More details can be found in Zhao et al. [sent-411, score-0.183]

81 This motivates our choice of the smooth-projected neighborhood pursuit approach. [sent-413, score-0.572]

82 The smooth-projected neighborhood pursuit generates 6 mid-size modules and 6 small modules, while the naive neighborhood pursuit generated 1 large module, 2 mid-size modules and 6 small modules. [sent-415, score-1.382]

83 The nonparanormal approach discovers more refined structures and improves the interpretability of the obtained graph. [sent-416, score-0.481]

84 ; (3) Topics closely related to modern physics are clustered in the same module such as “quantum-29”, “magnetic-55”, ”pressure-92”, “solar-62”, etc. [sent-418, score-0.101]

85 In contrast, the naive neighborhood pursuit mixes all these different topics in a large module. [sent-420, score-0.723]

86 (a) Our Proposed Method (b) Naive Neighborhood Pursuit Figure 4: Two topic graphs illustrating the difference of the estimated topic graphs. [sent-421, score-0.162]

87 The smoothprojected neighborhood pursuit (subfigure (a)) generates 6 mid-size modules and 6 small modules while the naive neighborhood pursuit (subfigure (b)) generates 1 large module, 2 mid-size modules and 6 small modules. [sent-422, score-1.453]

88 7 Conclusion and Acknowledgement In this paper, we study how to estimate the nonparanormal graph using the neighborhood pursuit in conjunction with the possible indefinite nonparanormal skeptic estimator. [sent-423, score-2.052]

89 Using our proposed smoothed projection approach, the resulting estimator can be used as a positive semi-definite refinement of the nonparanormal skeptic estimator. [sent-424, score-1.141]

90 Our estimator has better graph estimation performance with theoretical guarantee. [sent-425, score-0.256]

91 Our results suggest that it is possible to gain estimation robustness and modeling flexibility without losing two important computational structures: convexity and smoothness. [sent-426, score-0.133]

92 A smoothing proximal gradient method for general structured sparse regression. [sent-447, score-0.194]

93 Efficient estimation in the bivariate normal copula model: Normal margins are least-favorable. [sent-472, score-0.132]

94 The nonparanormal: Semiparametric estimation of high dimensional undirected graphs. [sent-491, score-0.131]

95 Stability approach to regularization selection for high dimensional graphical models. [sent-497, score-0.129]

96 Sparse graphical gaussian modeling of the isoprenoid gene network in arabidopsis thaliana. [sent-556, score-0.122]

97 Model selection and estimation in the gaussian graphical model. [sent-561, score-0.169]

98 The huge package for highdimensional undirected graph estimation in r. [sent-574, score-0.239]

99 A smoothing projection approach for high dimensional nonparanormal graph estimation. [sent-580, score-0.804]

100 Adaptive lasso for high dimensional regression and gaussian graphical modeling. [sent-588, score-0.212]


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