Performability measure for acyclic Markovian models

AbstractContinuous-time Markov processes with a finite-state space are generally considered to model degradable fault-tolerant computer systems. The finite space is partitioned as ∪mi=1 Bi, where Bi stands for the set of states which corresponds to the configuration where the system has a performance level (or reward rate) equal to τi. The performability Yt is defined as the accumulated reward over a mission time [0, t]. In this paper, a renewal equation is established for the performability measure and solved for both “standard” and uniform acyclic models. Two closed form expressions for the performability measure are derived for the two types of models. Furthermore, an algorithm with a low polynomial computational complexity is presented and applied to a degradable computer system

Reforms and Growth in MENA Countries:New Empirical Evidence

In this paper we empirically analyze the linkages among economic reforms, human capital, physical infrastructure, and growth for a panel of 44 developing countries over 1970-80 to 1999. For this purpose, we generate aggregated reform indicators using principal component analysis. We show that the growth performance of the MENA region has been disappointing because these economies have lagged behind in terms of economic reforms. However, our analysis also reveals that the growth dividend of some reforms has been small. This is the case when structural reforms are implemented in an unstable macroeconomic environment (which corresponds to the situation of the MENA countries in the 1980s), and when macroeconomic reforms are accompanied by a low level of structural reforms (as observed during the 1990s). Our result illustrates the complementarities between reforms as modeled by Mussa (1987) and Williamson (1994). Actually, after human capital and physical infrastructure, our analysis finds that macroeconomic and external stability are key variables for the reform process and for the growth prospects of the developing world.

Governance and Private Investment in the Middle East and North Africa

This paper addresses the issue of the low level of private investment in the Middle East and North Africa (MENA) region, with special emphasis on the role of governance. Based on the existing literature, we have categorized what types of governance institutions are more detrimental to entrepreneurial investments. We have then estimated a simultaneous model of private investment and governance quality where economic policies concurrently explain both variables. Our empirical results show that governance plays a significant role in private investment decisions. This result is particularly true in the case of “Administrative Quality” in the form of control of corruption, bureaucratic quality, investment-friendly profile of administration, and law and order, as well as for “Political Stability”. Evidence in favor of “Public Accountability” seems, however, less robust. Our estimations also stress that structural reforms -- such as financial development and trade openness – and human development affect private investment decisions directly, and/or through their positive impact on governance. These findings bring new empirical evidence on the subject of private investment in the developing world and in MENA countries in particular.governance, private investment, institutions, Middle East and North Africa.

Public infrastructure and private investment in the Middle East and North Africa

The authors examine the impact of public infrastructure on private capital formation in three countries of the Middle East and North Africa-Egypt, Jordan, and Tunisia. They highlight various channels through which public infrastructure may affect private investment. Then they describe their empirical framework, which is based on a vector autoregression (VAR) model that accounts for flows and (quality-adjusted) stocks of public infrastructure, private investment, as well as changes in output, private sector credit, and the real exchange rate. The authors propose two aggregate measures of the quality of public infrastructure and use principal components to derive a composite indicator. Their analysis suggests that public infrastructure has both"flow"and"stock"effects on private investment in Egypt, but only a"stock"effect in Jordan and Tunisia. But these effects are small and short-lived, reflecting the unfavorable environment for private investment in their sample of countries. Reducing unproductive public capital expenditure and improving quality must be accompanied by policy reforms aimed at limiting investment to infrastructure capital that crowds in the private sector and corrects for fundamental market failures. This will entail privatization and greater involvement of the private sector in infrastructure investment. While infrastructure (in the form of the provision of critical telecommunications, transport, and energy services) is important, other improvements in the environment in which domestic investment is conducted are crucial. These include the need to provide financing on adequate terms and guarantee a secure and efficient justice system.

Curriculum learning for multilevel budgeted combinatorial problems

Learning heuristics for combinatorial optimization problems through graph neural networks have recently shown promising results on some classic NP-hard problems. These are single-level optimization problems with only one player. Multilevel combinatorial optimization problems are their generalization, encompassing situations with multiple players taking decisions sequentially. By framing them in a multi-agent reinforcement learning setting, we devise a value-based method to learn to solve multilevel budgeted combinatorial problems involving two players in a zero-sum game over a graph. Our framework is based on a simple curriculum: if an agent knows how to estimate the value of instances with budgets up to $B$, then solving instances with budget $B+1$ can be done in polynomial time regardless of the direction of the optimization by checking the value of every possible afterstate. Thus, in a bottom-up approach, we generate datasets of heuristically solved instances with increasingly larger budgets to train our agent. We report results close to optimality on graphs up to $100$ nodes and a $185 \times$ speedup on average compared to the quickest exact solver known for the Multilevel Critical Node problem, a max-min-max trilevel problem that has been shown to be at least $\Sigma_2^p$-hard

Exchange Rate Management within the Middle East and North Africa Region:The Cost to Manufacturing Competitiveness

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Governance and private investment in the Middle East and North Africa

This paper addresses the issue of the low level of private investment in the Middle East and North Africa (MENA) region, with special emphasis on the role of governance. Based on the existing literature, the authors categorize what types of governance institutions are more detrimental to entrepreneurial investments. They then estimate a simultaneous model of private investment and governance quality where economic policies concurrently explain both variables. The empirical results show that governance plays a significant role in private investment decisions. This result is particularly true in the case of"administrative quality"in the form of control of corruption, bureaucratic quality, investment-friendly profile of administration, and law and order, as well as for"political stability."Evidence in favor of"public accountability"seems, however, less robust. The estimations also stress that structural reforms-such as financial development and trade openness-and human development affect private investment decisions directly, and/or through their positive impact on governance. These findings bring new empirical evidence on the subject of private investment in the developing world and in MENA countries in particular.Governance Indicators,Investment and Investment Climate,Economic Theory&Research,National Governance,Trade and Regional Integration