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Fast Projection onto the Capped Simplex with Applications to Sparse Regression in Bioinformatics

Neural Information Processing Systems

We consider the problem of projecting a vector onto the so-called k-capped simplex, which is a hyper-cube cut by a hyperplane. For an n-dimensional input vector with bounded elements, we found that a simple algorithm based on Newton's method is able to solve the projection problem to high precision with a complexity roughly about O(n), which has a much lower computational cost compared with the existing sorting-based methods proposed in the literature. We provide a theory for partial explanation and justification of the method. We demonstrate that the proposed algorithm can produce a solution of the projection problem with high precision on large scale datasets, and the algorithm is able to significantly outperform the state-of-the-art methods in terms of runtime (about 6-8 times faster than a commercial software with respect to CPU time for input vector with 1 million variables or more). We further illustrate the effectiveness of the proposed algorithm on solving sparse regression in a bioinformatics problem. Empirical results on the GWAS dataset (with 1,500,000 single-nucleotide polymorphisms) show that, when using the proposed method to accelerate the Projected Quasi-Newton (PQN) method, the accelerated PQN algorithm is able to handle huge-scale regression problem and it is more efficient (about 3-6 times faster) than the current state-of-the-art methods.




Appendices ALow-Rank Matrix Factorization with Non-Uniform Sampling

Neural Information Processing Systems

In this section, we demonstrate the effectiveness of low-rank matrix factorization in recovering the label relationship matrix. We first present four important facts: f1: the rank of the matrix is equivalent to the number of classes. Specifically, this also means that if ห†Zi,k = 1, then ห†Zj,k = 1. We consider a toy example (without self-loops), ห†Z = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A = 0 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0 (14) In a standard LRMF problem, it is not possible to recover ห†Z from A since no entries are observed for the third and fourth rows. However, we can demonstrate how LRMF effectively performs in this situation. Recovery: We begin by assuming v1 is in class 1, resulting in U1,: = [1, 1, 1] and V1,: = [1,0,0]. By observing A1,4, we know that v4 is also in class 1, resulting in U4,: = [1, 1, 1]and V4,: = [1,0,0](f2). By analyzing A1,2 and A1,3, we determine that v2 and v3 do not belong to class 1.





Malicious client Benign client Subspace distributionModel distribution

Neural Information Processing Systems

This poison-coupling the modifies poison-coupling paper the presents training effect Lockdo ef protocol in fect. FL, wn, which Lockdo by an isolating isolated significantly wn follo subspace the ws de training three grades training ke the subspaces y procedures.


6 Appendix

Neural Information Processing Systems

Table 9 compares these abstracts to the corresponding examples from Tables I.25-27 in section I of [46]. The abstracts are decoded using greedy algorithm with temperature T = 0.5.