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Poster
Spectral Norm Regularization of Orthonormal Representations for Graph Transduction
Rakesh Shivanna · Bibaswan K Chatterjee · Raman Sankaran · Chiranjib Bhattacharyya · Francis Bach
Recent literature~\cite{ando} suggests that embedding a graph on an unit sphere leads to better generalization for graph transduction. However, the choice of optimal embedding and an efficient algorithm to compute the same remains open. In this paper, we show that orthonormal representations, a class of unitsphere graph embeddings are PAC learnable. Existing PACbased analysis do not apply as the VC dimension of the function class is infinite. We propose an alternative PACbased bound, which do not depend on the VC dimension of the underlying function class, but is related to the famous Lov\'{a}sz~$\vartheta$ function. The main contribution of the paper is SPORE, a SPectral regularized ORthonormal Embedding for graph transduction, derived from the PAC bound. SPORE is posed as a nonsmooth convex function over an \emph{elliptope}. These problems are usually solved as semidefinite programs (SDPs) with time complexity $O(n^6)$. We present, Infeasible Inexact proximal~(IIP): an Inexact proximal method which performs subgradient procedure on an approximate projection, not necessarily feasible. IIP is more scalable than SDP, has an $O(\frac{1}{\sqrt{T}})$ convergence, and is generally applicable whenever a suitable approximate projection is available. We use IIP to compute SPORE where the approximate projection step is computed by FISTA, an accelerated gradient descent procedure. We show that the method has a convergence rate of $O(\frac{1}{\sqrt{T}})$. The proposed algorithm easily scales to 1000's of vertices, while the standard SDP computation does not scale beyond few hundred vertices. Furthermore, the analysis presented here easily extends to the multiple graph setting.
Author Information
Rakesh Shivanna (Google Inc.)
Bibaswan K Chatterjee (Indian Institute of Science)
Raman Sankaran (Indian Institute of Science)
Chiranjib Bhattacharyya (Indian Institute of Science)
Francis Bach (INRIA  ENS)
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