On using an improved Benders method for cell suppression

The cell suppression problem (CSP) is one of the most widely applied methods for tabular data protection. Given a set of primary cells to be protected, CSP aims at finding a set of secondary cells to be additionally removed to guarantee that estimates of values of primary cells fall out of a predefined protection interval. From a computational point of view, CSP is very challenging even for tables of moderate size and number of primary cells. Currently, the only effective optimal approach for CSP is Benders decomposition (also known as cutting planes). However, the convergence to the optimal solution is often too slow due to well known instability issues of Benders decomposition. This work discusses a recently developed improved Benders method, which focus on finding new solutions in the neighborhood of ”good” points. Some results are reported in the solution of realistic and real-world CSP instances, showing the effectiveness of this approachPeer ReviewedPostprint (author's final draft

A Distributional Analysis of the Gender Wage Gap in Bangladesh

This paper decomposes the gender wage gap along the entire wage distribution into an endowment effect and a discrimination effect, taking into account possible selection into full-time employment. Applying a new decomposition approach to the Bangladesh Labour Force Survey (LFS) data we find that women are paid less than men every where on the wage distribution and the gap is higher at the lower end of the distribution. Discrimination against women is the primary determinant of the wage gap. We also find that the gap has widened over the period 1999 - 2005. Our results intensify the call for better enforcement of gender based affirmative action policies.Gender wage Gap, Discrimination Effect, Selection, Unconditional Quantile Regression, Bangladesh

On dual Schur domain decomposition method for linear first-order transient problems

This paper addresses some numerical and theoretical aspects of dual Schur domain decomposition methods for linear first-order transient partial differential equations. In this work, we consider the trapezoidal family of schemes for integrating the ordinary differential equations (ODEs) for each subdomain and present four different coupling methods, corresponding to different algebraic constraints, for enforcing kinematic continuity on the interface between the subdomains. Method 1 (d-continuity) is based on the conventional approach using continuity of the primary variable and we show that this method is unstable for a lot of commonly used time integrators including the mid-point rule. To alleviate this difficulty, we propose a new Method 2 (Modified d-continuity) and prove its stability for coupling all time integrators in the trapezoidal family (except the forward Euler). Method 3 (v-continuity) is based on enforcing the continuity of the time derivative of the primary variable. However, this constraint introduces a drift in the primary variable on the interface. We present Method 4 (Baumgarte stabilized) which uses Baumgarte stabilization to limit this drift and we derive bounds for the stabilization parameter to ensure stability. Our stability analysis is based on the ``energy'' method, and one of the main contributions of this paper is the extension of the energy method (which was previously introduced in the context of numerical methods for ODEs) to assess the stability of numerical formulations for index-2 differential-algebraic equations (DAEs).Comment: 22 Figures, 49 pages (double spacing using amsart

A Second Order Finite Volume Technique for Simulating Transport in Anisotropic Media

An existing two-dimensional finite volume technique is modified by introducing a correction term to increase the accuracy of the method to second order. It is well known that the accuracy of the finite volume method strongly depends on the order of the approximation of the flux term at the control volume (CV) faces. For highly orthotropic and anisotropic media, first order approximations produce inaccurate simulation results, which motivates the need for better estimates of the flux expression. In this article, a new approach to approximate the flux term at the CV face is presented. The discretisation involves a decomposition of the flux and an improved least squares approximation technique to calculate the derivatives of the dependent function on the CV faces for estimating both the cross diffusion term and a correction for the primary flux term. The advantage of this method is that any arbitrary unstructured mesh can be used to implement the technique without considering the shapes of the mesh elements. It was found that the numerical results well matched the available exact solution for a representative transport equation in highly orthotropic media and the benchmark solutions obtained on a fine mesh for anisotropic media. Previously proposed CV techniques are compared with the new method to highlight its accuracy for different unstructured meshes

Interactive boundary element analysis for engineering design.

Structural design of mechanical components is an iterative process that involves multiple stress analysis runs; this can be time consuming and expensive. Significant improvements in the eciency of this process can be made by increasing the level of interactivity. One approach is through real-time re-analysis of models with continuously updating geometry. Three primary areas need to be considered to accelerate the re-solution of boundary element problems. These are re-meshing the model, updating the boundary element system of equations and re-solution of the system. Once the initial model has been constructed and solved, the user may apply geometric perturbations to parts of the model. The re-meshing algorithm must accommodate these changes in geometry whilst retaining as much of the existing mesh as possible. This allows the majority of the previous boundary element system of equations to be re-used for the new analysis. For this problem, a GMRES solver has been shown to provide the fastest convergence rate. Further time savings can be made by preconditioning the updated system with the LU decomposition of the original system. Using these techniques, near real-time analysis can be achieved for 3D simulations; for 2D models such real-time performance has already been demonstrated

Globalization, De-Industrialization and Mexican Exceptionalism 1750-1879

Like the rest of the poor periphery, Mexico had to deal with de-industrialization forces between 1750 and 1913, those critical 150 years when the economic gap between the industrial core and the primary-product-producing periphery widened to such huge dimensions. Yet, from independence to mid-century Mexico did better on this score than did most countries around the periphery. This paper explores the sources of Mexican exceptionalism with de-industrialization. It decomposes those sources into those attributable to productivity events in the core and to globalization forces connecting core to periphery, and to those attributable to domestic forces specific to Mexico. It uses a neo-Ricardian model (with non-tradable foodstuffs) to implement the decomposition, and advocates a price dual approach, and develops a new price and wage data base 1750-1878. There were three forces at work that account for Mexican exceptionalism: first, the terms of trade and Dutch disease effects were much weaker; second, Mexico maintained secular wage competitiveness with the core; and third, Mexico had the autonomy to devise effective ways to foster industry. The first appears to have been the most important.