3,497 research outputs found
Simplex basis function based sparse least squares support vector regression
In this paper, a novel sparse least squares support vector regression algorithm, referred to as LSSVR-SBF, is
introduced which uses a new low rank kernel based on simplex basis function, which has a set of nonlinear parameters.
It is shown that the proposed model can be represented as a sparse linear regression model based on simplex basis
functions. We propose a fast algorithm for least squares support vector regression solution at the cost of O(N) by
avoiding direct kernel matrix inversion. An iterative estimation algorithm has been proposed to optimize the nonlinear parameters associated with the simplex basis functions with the aim of minimizing model mean square errors using the gradient descent algorithm. The proposed fast least square solution and the gradient descent algorithm are alternatively applied. Finally it is shown that the model has a dual representation as a piecewise linear model with respect to the
system input. Numerical experiments are carried out to demonstrate the effectiveness of the proposed approaches
Level Set Methods for Stochastic Discontinuity Detection in Nonlinear Problems
Stochastic physical problems governed by nonlinear conservation laws are
challenging due to solution discontinuities in stochastic and physical space.
In this paper, we present a level set method to track discontinuities in
stochastic space by solving a Hamilton-Jacobi equation. By introducing a speed
function that vanishes at discontinuities, the iso-zero of the level set
problem coincide with the discontinuities of the conservation law. The level
set problem is solved on a sequence of successively finer grids in stochastic
space. The method is adaptive in the sense that costly evaluations of the
conservation law of interest are only performed in the vicinity of the
discontinuities during the refinement stage. In regions of stochastic space
where the solution is smooth, a surrogate method replaces expensive evaluations
of the conservation law. The proposed method is tested in conjunction with
different sets of localized orthogonal basis functions on simplex elements, as
well as frames based on piecewise polynomials conforming to the level set
function. The performance of the proposed method is compared to existing
adaptive multi-element generalized polynomial chaos methods
Sparsity Constrained Nonlinear Optimization: Optimality Conditions and Algorithms
This paper treats the problem of minimizing a general continuously
differentiable function subject to sparsity constraints. We present and analyze
several different optimality criteria which are based on the notions of
stationarity and coordinate-wise optimality. These conditions are then used to
derive three numerical algorithms aimed at finding points satisfying the
resulting optimality criteria: the iterative hard thresholding method and the
greedy and partial sparse-simplex methods. The first algorithm is essentially a
gradient projection method while the remaining two algorithms are of coordinate
descent type. The theoretical convergence of these methods and their relations
to the derived optimality conditions are studied. The algorithms and results
are illustrated by several numerical examples.Comment: submitted to SIAM Optimizatio
Randomized Sketches of Convex Programs with Sharp Guarantees
Random projection (RP) is a classical technique for reducing storage and
computational costs. We analyze RP-based approximations of convex programs, in
which the original optimization problem is approximated by the solution of a
lower-dimensional problem. Such dimensionality reduction is essential in
computation-limited settings, since the complexity of general convex
programming can be quite high (e.g., cubic for quadratic programs, and
substantially higher for semidefinite programs). In addition to computational
savings, random projection is also useful for reducing memory usage, and has
useful properties for privacy-sensitive optimization. We prove that the
approximation ratio of this procedure can be bounded in terms of the geometry
of constraint set. For a broad class of random projections, including those
based on various sub-Gaussian distributions as well as randomized Hadamard and
Fourier transforms, the data matrix defining the cost function can be projected
down to the statistical dimension of the tangent cone of the constraints at the
original solution, which is often substantially smaller than the original
dimension. We illustrate consequences of our theory for various cases,
including unconstrained and -constrained least squares, support vector
machines, low-rank matrix estimation, and discuss implications on
privacy-sensitive optimization and some connections with de-noising and
compressed sensing
- …