11 research outputs found
Implementation of a fixing strategy and parallelization in a recent global optimization method
Electromagnetism-like Mechanism (EM) heuristic is a population-based stochastic global optimization method inspired by the attraction-repulsion mechanism of the electromagnetism theory. EM was originally proposed for solving continuous global optimization problems with bound constraints and it has been shown that the algorithm performs quite well compared to some other global optimization methods. In this work, we propose two extensions to improve the performance of the original algorithm: First, we introduce a fixing strategy that provides a mechanism for not being trapped in local minima, and thus, improves the effectiveness of the search. Second, we use the proposed fixing strategy to parallelize the algorithm and utilize a cooperative parallel search on the solution space. We then evaluate the performance of our study under three criteria: the quality of the solutions, the number of function evaluations and the number of local minima obtained. Test problems are generated by an algorithm suggested in the literature that builds test problems with varying degrees of difficulty. Finally, we benchmark our results with that of the
Knitro solver with the multistart option set
A symmetric rank-one Quasi-Newton line-search method using negative curvature directions
We propose a quasi-Newton line-search method that uses negative curvature directions for solving unconstrained optimization problems. In this method, the symmetric rank-one (SR1) rule is used to update the Hessian approximation. The SR1 update rule is known to have a good numerical performance; however, it does not guarantee positive definiteness of the updated matrix. We first discuss the details of the proposed algorithm and then concentrate on its numerical efficiency. Our extensive computational study shows the potential of the proposed method from different angles, such as; its second order convergence behavior, its exceeding performance when compared to two other existing packages, and its computation profile illustrating the possible bottlenecks in the execution time. We then conclude the paper with the convergence analysis of the proposed method
An Inexact Successive Quadratic Approximation Method for Convex L-1 Regularized Optimization
We study a Newton-like method for the minimization of an objective function
that is the sum of a smooth convex function and an l-1 regularization term.
This method, which is sometimes referred to in the literature as a proximal
Newton method, computes a step by minimizing a piecewise quadratic model of the
objective function. In order to make this approach efficient in practice, it is
imperative to perform this inner minimization inexactly. In this paper, we give
inexactness conditions that guarantee global convergence and that can be used
to control the local rate of convergence of the iteration. Our inexactness
conditions are based on a semi-smooth function that represents a (continuous)
measure of the optimality conditions of the problem, and that embodies the
soft-thresholding iteration. We give careful consideration to the algorithm
employed for the inner minimization, and report numerical results on two test
sets originating in machine learning
Parallel algorithms for nonlinear optimization
Parallel algorithm design is a very active research topic in optimization as parallel computer architectures have recently become easily accessible. This thesis is about an approach for designing parallel nonlinear programming algorithms. The main idea is to benefit from parallelization in designing new algorithms rather than considering direct parallelizations of the existing methods. We give a general framework following our approach, and then, give distinct algorithms that fit into this framework. The example algorithms we have designed either use procedures of existing methods within a multistart scheme, or they are completely new inherently parallel algorithms. In doing so, we try to show how it is possible to achieve parallelism in algorithm structure (at different levels) so that the resulting algorithms have a good solution performance in terms of robustness, quality of steps, and scalability. We complement our discussion with convergence proofs of the proposed algorithms
Bolstering Stochastic Gradient Descent with Model Building
Stochastic gradient descent method and its variants constitute the core
optimization algorithms that achieve good convergence rates for solving machine
learning problems. These rates are obtained especially when these algorithms
are fine-tuned for the application at hand. Although this tuning process can
require large computational costs, recent work has shown that these costs can
be reduced by line search methods that iteratively adjust the stepsize. We
propose an alternative approach to stochastic line search by using a new
algorithm based on forward step model building. This model building step
incorporates second-order information that allows adjusting not only the
stepsize but also the search direction. Noting that deep learning model
parameters come in groups (layers of tensors), our method builds its model and
calculates a new step for each parameter group. This novel diagonalization
approach makes the selected step lengths adaptive. We provide convergence rate
analysis, and experimentally show that the proposed algorithm achieves faster
convergence and better generalization in well-known test problems. More
precisely, SMB requires less tuning, and shows comparable performance to other
adaptive methods
Distributed algorithms for delay bounded minimum energy wireless broadcasting
In many network applications, broadcasting is an important part of the operation where data generated by a source is disseminated to all users in the network. Judicious use of limited energy resources in wireless networks typically requires routing packets along the branches of a tree spanning the source and the destination nodes. In addition, networks that support real-time traffic are also required to provide certain quality of service (QoS) guarantees in terms of the end-to-end delay along the individual paths from the source to each of the destination nodes. Therefore, in this paper we focus on constructing a minimum power broadcast tree with a maximum depth D which corresponds to the maximum tolerable end-to-end delay in the network. We investigate two different distributed algorithms for this purpose: Distributed Tree Expansion (DTE) and Distributed Link Substitution (DLS). DTE is based on an implementation of a distributed minimum spanning tree algorithm in which
the tree grows at each iteration by adding a node that can cover the maximum number of currently uncovered nodes in the network with minimum incremental transmission power and without violating the delay constraint. In DLS, we begin
with a feasible broadcast tree, and then improve that solution by replacing expensive transmissions by transmissions at lower power levels while preserving the feasibility of the tree with respect to the delay bound. Hence, DTE is constructive in nature while DLS is an improvement algorithm. Although DTE increases the message complexity to O(n^3) from O(n^2) in a network of
size n, it provides up to 50% improvement in total expended power compared to DLS
MEDITERRANEAN SPOTTED FEVER DUE TO CONTACT WITH DOG-TICK
WOS: 000260856700022PubMed: 19149095Mediterranean spotted fever (MSF) is one of the tick-borne rickettsial infections caused by Rickettsia conorii. It is transmitted to humans by brown dog ticks (Rhipicephalus sanguineus). In this case report, a 16-years-old male patient who was diagnosed as MSF after an exposure to dog-tick in Bartin province (located at middle Black Sea region of Turkey) has been presented. His history revealed that, five days before admission to the hospital (on June, 2007) he had cleaned dog-ticks from his dog, and after 12 hours he found a stucked tick on his leg and he took it out right away with a tweezer. High fever, headache and generalized maculopapular rash including soles and palms and a black-colored lesion at the tick bite site developed three days later. In clinical examination, there was a black escar circled with a red-purple colored halo in front of the right tibia at the site of the tick bite showing high similarity to "tache noire" which was specific to MSF. Indirect immunofluorescence assay (IPA) for Rickettsia yielded negative result in the serum sample collected on admission day, however, it was found positive at 1/512 titer in the serum sample collected 10 days after admission. The patient has recovered completely without any complication after 10 days of doxycycline therapy. The aim of this presentation is to point out that MSF should be considered for the differential diagnosis of a patient with a history of tick bite, fever, maculopapular rash, headache, myalgia, arthralgia and especially with black escar during summer months in our country where the incidence of tick-borne infections has been increasing since recent years