Thursday, May 14, 2015

Newton Sketch: A Linear-time Optimization Algorithm with Linear-Quadratic Convergence

Another sketching algorithm using random projection this week:

Newton Sketch: A Linear-time Optimization Algorithm with Linear-Quadratic Convergence by Mert Pilanci, Martin J. Wainwright

We propose a randomized second-order method for optimization known as the Newton Sketch: it is based on performing an approximate Newton step using a randomly projected or sub-sampled Hessian. For self-concordant functions, we prove that the algorithm has super-linear convergence with exponentially high probability, with convergence and complexity guarantees that are independent of condition numbers and related problem-dependent quantities. Given a suitable initialization, similar guarantees also hold for strongly convex and smooth objectives without self-concordance. When implemented using randomized projections based on a sub-sampled Hadamard basis, the algorithm typically has substantially lower complexity than Newton's method. We also describe extensions of our methods to programs involving convex constraints that are equipped with self-concordant barriers. We discuss and illustrate applications to linear programs, quadratic programs with convex constraints, logistic regression and other generalized linear models, as well as semidefinite programs.
h/t Suresh for the find.
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1 comment:

Royi said...

Do they have a MATLAB implementation?
This is what I don't like on Arxiv, it doesn't allow spreading code.