Novel linear programming approach for building a piecewise nonlinear binary classifier with a priori accuracy
* Co-authored with Ubaldo Manuel García Palomares.
* Published in "Decision Support Systems", on feb-2012
This paper describes a novel approach to build a piecewise (non)linear surface that separates individuals from two... more
This paper describes a novel approach to build a piecewise (non)linear surface that separates individuals from two classes with an a priori classification accuracy. In particular, total classification with a good generalization level can be obtained, provided no individual belongs to both classes. The method is iterative: at each iteration a new piece of the surface is found via the solution of a Linear Programming model. Theoretically, the larger the number of iterations, the better the classification accuracy in the training set; numerically, we also found that the generalization ability does not deteriorate on the cases tested. Nonetheless, we have included a procedure that computes a lower bound to the number of errors that will be generated in any given validation set. If needed, an early stopping criterion is provided. We also showed that each piece of the discriminating surface is equivalent to a neuron of a feed forward neural network (FFNN); so as a byproduct we are providing a novel training scheme for FFNNs that avoids the minimization of non convex functions which, in general, present many local minima.
We compare this algorithm with a new linear SVM that needs no pre tuning and has an excellent performance on standard and synthetic data. Highly encouraging numerical results are reported on synthetic examples, on the Japanese Bank dataset, and on medium and small datasets from the Irvine repository of machine learning databases.rly stopping criteria is provided. We also showed that each piece of the discriminating surface is equivalent to a neuron of a feed
forward neural network (FFNN); so as a byproduct we are providing a novel training scheme for FFNNs that avoids the minimization of flat non convex functions which, in general, present many local minima. High encouraging numerical results are reported on a synthetic example, on the Japanese Bank
dataset, and on medium and small datasets from the Irvine repository of machine learning databases.
Inverse optimization with endogenous arrival time constraints to calibrate the household activity pattern problem
by Joseph Chow
Chow, J.Y.J., Recker, W.W., 2012. Inverse optimization with endogenous arrival time constraints to calibrate the household activity pattern problem, Transportation Research Part B 46(3), 463-479.
A parameter estimation method is proposed for calibrating the household activity pattern problem so that it can be... more A parameter estimation method is proposed for calibrating the household activity pattern problem so that it can be used as a disaggregate, activity-based analog of the traffic assignment problem for activity-based travel forecasting. Inverse optimization is proposed for estimating parameters of the household activity pattern problem such that the observed behavior is optimal, the patterns can be replicated, and the distribution of the parameters is consistent. In order to fit the model to both the sequencing of activities and the arrival times to those activities, an inverse problem is formulated as a mixed integer linear programming problem such that coefficients of the objectives are jointly estimated along with the goal arrival times to the activities. The formulation is designed to be structurally similar to the equivalent problems defined by Ahuja and Orlin and can be solved exactly with a cutting plane algorithm. The concept of a unique invariant common prior is used to regularize the estimation method, and proven to converge using the Method of Successive Averages. The inverse model is tested on sample households from the 2001 California Household Travel Survey and results indicate a significant improvement over the standard inverse problem in the literature as well as baseline prescriptive models that do not make use of sample data for calibration. Although, not unexpectedly, the estimated optimization model by itself is a relatively poor forecasting model, it may be used in determining responses of a population to spatio-temporal scenarios where revealed preference data is absent.
Solving the Recognition Problem for Six Lines Using the Dixon Resultant
by Robert Lewis
coauthor Peter Stiller. MATCOM 49 (1999)
The “Six-Line Problem” arises in computer vision and in the automated analysis of images. Given a three-dimensional... more The “Six-Line Problem” arises in computer vision and in the automated analysis of images. Given a three-dimensional object, one extracts geometric features (for example six lines) and then, via techniques from algebraic geometry and geometric invariant theory, produces a set of three-dimensional invariants that represents that feature set. Suppose that later an object is encountered in an image. (For example a photograph taken by a camera modeled by standard perspective projection, i.e. a “pinhole” camera.) Suppose further that six lines are extracted from the object appearing in the image.The problem is to decide if the object in the image is the original 3D object.To answer this question two-dimensional invariants are computed from the lines in the image.One can show that conditions for geometric consistency between the three-dimensional object features and the two dimensional image features can be expressed as a set of polynomial equations in the combined set of two and three dimensional invariants.The object in the image is geometrically consistent with the original object if the set of equations has a solution.One well known method to attack such sets of equations is with resultants. Unfortunately, the size and complexity of this problem made it appear overwhelming until recently. This paper will describe a solution obtained using our own variant of the Cayley-Dixon-Kapur-Saxena-Yang resultant. There is reason to suspect that the resultant technique we employ here may solve other complex polynomial systems.
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Seen by:Heuristics to Accelerate the Dixon Resultant
by Robert Lewis
published in MATCOM 77, Issue 4, April 2008
The Dixon Resultant method solves a system of polynomial equations by computing its resultant. It... more
The Dixon Resultant method solves a system of polynomial equations by computing its resultant. It constructs a square matrix whose determinant det is a multiple of the resultant res. The naive way to proceed is to compute det, factor it, and identify res. But often det is too large to compute or factor, even though res is relatively small.
In this paper we describe three heuristic methods that often overcome these problems. The first, although sometimes useful by itself, is often a subprocedure of the second two. The second may be used on any polynomial system to discover factors of det without producing the complete determinant. The third applies when res appears as a factor of det in a certain exponential pattern. This occurs in some symmetrical systems of equations. We show examples from computational chemistry, signal processing, dynamical systems, quantifier elimination, and pure mathematics.
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Seen by:The Dixon Resultant
by Robert Lewis
expository paper
This is an expository paper explaining the Dixon resultant, as extended by Kapur, Saxena, and Yang.
In most... more
This is an expository paper explaining the Dixon resultant, as extended by Kapur, Saxena, and Yang.
In most circumstances, this is the method of choice in solving systems of multivariate polynomials. I would except from that statement very large systems that come up in cryptography.
Fermat code to run Dixon can be found here:
http://home.bway.net/lewis/dixon
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Seen by:Algorithmic Search for Flexibility using Resultants of Polynomial Systems
by Robert Lewis
coauthor E. Coutsias. published in Automated Deduction in Geometry. Lecture Notes in Computer Science, Vol. 4869, p. 68 - 79. Springer
This paper describes the recent convergence of four topics: polynomial systems, flexibility of three dimensional... more This paper describes the recent convergence of four topics: polynomial systems, flexibility of three dimensional objects, computational chemistry, and computer algebra. We discuss a way to solve systems of polynomial equations with resultants. Using ideas of Bricard, we find a system of polynomial equations that models a configuration of quadrilaterals that is equivalent to some three dimensional structures. These structures are of interest in computational chemistry, as they represent molecules. We then describe an algorithm that examines the resultant and determines ways that the structure can be flexible.
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