Using column generation to solve extensions to the Markowitz model

Abstract

We introduce a solution scheme for portfolio optimization problems with cardinality constraints. Typical portfolio optimization problems are extensions of the classical Markowitz mean–variance portfolio optimization model. We solve such types of problems using a method similar to column generation. In this scheme, the original problem is restricted to a subset of the assets resulting in a master convex quadratic problem. Then the dual information of the master problem is used in a subproblem to propose more assets to consider. We also consider other extensions to the Markowitz model to diversify the portfolio selection within given intervals for active weights.     

Employment and SMEs during crises

The persistent increasing duration of unemployment has become an issue during economic crises. Although lay-offs at large firms normally make headlines during crises, we still know little about the potential impact of firm size on adjustment behavior in a crisis. We studied effects of firm size on employment growth during economic slowdowns using a rich microeconomic database for the 1988–2007 period in Portuguese manufacturing industry. The results show that economic downturns affect firm growth negatively. This negative effect is found to be higher for larger firms, both during and immediately following crisis periods. Small and medium-sized enterprises (SMEs) emerge as potential stabilizers in downturn periods. However, larger firms seem to be able to quickly recover from downturn periods. Our results contribute to the scarce literature and to the understanding of the Portuguese case, where many SMEs secure most jobs. These first results may be useful, because SMEs play a determinant role in other European Union economies.     

The lesson and warning of a crisis foretold: a political economy approach

The financial crisis, which began in summer 2007 in the USA and then spread contagiously throughout the rest of the world, is systemic in nature. Indeed, it is not a local or regional crisis. It is the inevitable starting point of a process which for more than 30 years has changed at its very roots the financial way of being and doing, thus undermining the very bases of that liberal social order which is at the core of Western civilization. The nature of the causes of the crisis is twofold: those immediate, which speak of the specific characteristics adopted in recent times by the financial markets, and those remote, which blame aspects of the cultural matrix which accompanied the transition from industrial to financial capitalism. From the moment that epoch-making phenomenon which we call globalization began to take shape, finance not only constantly increased its quota of activity in the economic sphere, but it has also progressively contributed to transform both people’s cognitive maps and their value systems. It is to this latter that one refers today in speaking of the financialization of society. The article mainly deals with the remote causes of the crisis with the aim of showing the consequences of the misleading ideology diffused by mainstream economics, from which have drunk market agents, government political authorities and controlling agencies.      

Human resource management and developing proactive environmental strategies: The influence of environmental training and organizational learning

The need to implement advanced approaches to protect the environment is forcing companies to refocus their internal procedures and actions. To match employees' capabilities and the organization itself to these new requirements, the human resource management department can offer some key tools. This article analyzes whether environmental training (ET) and organizational learning (OL) positively influence the development of proactive environmental strategies (PESs) and compares the two processes, which differ in the time, costs, and difficulty required to implement them. Companies in the tourism sector are currently facing a highly dynamic environment where innovativeness is a decisive factor for achieving competitiveness. As such, we analyze whether the presence or absence of innovativeness influences the development of these two mechanisms. Using a sample of 252 tourism companies, we tested these relationships using structural equation modeling. The findings showed that (1) innovativeness is an antecedent of implementing ET and OL in the companies sampled, (2) both mechanisms promote implementing PESs, and (3) ET is equally as effective as OL for this purpose. Managers should take these findings into account when deciding which mechanism to apply when striving to achieve environmental proactivity.     

ARE LONG‐RUN PRICE STABILITY AND SHORT‐RUN OUTPUT STABILIZATION ALL THAT MONETARY POLICY CAN AIM FOR?

A central tenet of the so‐called new consensus view in macroeconomics is that there is no long‐run trade‐off between inflation and unemployment. The main policy implication of this principle is that all monetary policy can aim for is (modest) short‐run output stabilization and long‐run price stability, i.e. monetary policy is neutral with respect to output and employment in the long run. However, research on the different sources of path dependency in the economy suggests that persistent but nevertheless transitory changes in aggregate demand may have a permanent effect on output and employment. If this is the case, then, the way monetary policy is run does have long‐run effects on real variables. This paper provides an overview of this research and explores conceptually how monetary policy should be implemented once these long‐run effects are acknowledged.