Entropy evaluation sheds light on ecosystem complexity

Preserving biodiversity and ecosystem stability is a challenge that can be pursued through modern statistical mechanics modeling. Here we introduce a variational maximum entropy-based algorithm to evaluate the entropy in a minimal ecosystem on a lattice in which two species struggle for survival. The method quantitatively reproduces the scale-free law of the prey shoals size, where the simpler mean-field approach fails: the direct near neighbor correlations are found to be the fundamental ingredient describing the system self-organized behavior. Furthermore, entropy allows the measurement of structural ordering, that is found to be a key ingredient in characterizing two different coexistence behaviors, one where predators form localized patches in a sea of preys and another where species display more complex patterns. The general nature of the introduced method paves the way for its application in many other systems of interest.Comment: 13 pages, 5 figure

Ramsey monetary policy and international relative prices

We analyze welfare maximizing monetary policy in a dynamic two-country model with price stickiness and imperfect competition. In this context, a typical terms of trade externality affects policy interaction between independent monetary authorities. Unlike the existing literature, we remain consistent to a public finance approach by an explicit consideration of all the distortions that are relevant to the Ramsey planner. This strategy entails two main advantages. First, it allows an accurate characterization of optimal policy in an economy that evolves around a steady-state which is not necessarily efficient. Second, it allows to describe a full range of alternative dynamic equilibria when price setters in both countries are completely forward-looking and households' preferences are not restricted. In this context, we study optimal policy both in the long-run and along a dynamic path, and we compare optimal commitment policy under Nash competition and under cooperation. By deriving a second order accurate solution to the policy functions, we also characterize the welfare gains from international policy cooperation. Klassifikation: E52, F41 . This version: January, 2004. First draft: October 2003

EMU fiscal rules: Is there a gap?

The Stability and Growth Pact sets a medium-term target for fiscal policy of a budgetary position 'close to balance or in surplus'. This addition to the deficit rule defined by the Maastricht Treaty has been interpreted as an attempt to reconciliate the objective of sound public finances with the availability of adequate margins for stabilisation. However, with the debt rule set in the Treaty unchanged, there is a risk that the Pact will not fully achieve the desired reconciliation. Using the budget to implement stabilisation policy while still ensuring a reduction of the debt-to-GDP ratio during cyclical downturns, as required by the Treaty, is likely to require large structural surpluses. Assuming positive nominal growth rates, the closer the debt ratio is to 60 per cent the larger are the surpluses needed. If countries with debt ratios higher than 60 per cent set insufficiently ambitious deficit targets, they will not be able to make full use of the margins allowed by the 3 per cent threshold. During cyclical downturns such countries may have to adopt a pro-cyclical budgetary stance. The regulation of the interaction between deficit and debt rules is complicated by the EU definitions of debt and deficit, as they refer to different groups of transactions and are based on different accounting conventions.Fiscal Rules, Stabilisation Policy

Optimal monetary and fiscal policy in a currency union

We lay out a tractable model for fiscal and monetary policy analysis in a currency union, and study its implications for the optimal design of such policies. Monetary policy is conducted by a common central bank, which sets the interest rate for the union as a whole. Fiscal policy is implemented at the country level, through the choice of government spending. The model incorporates country-specific shocks and nominal rigidities. Under our assumptions, the optimal cooperative policy arrangement requires that inflation be stabilized at the union level by the common central bank, while fiscal policy is used by each country for stabilization purposes. By contrast, when the fiscal authorities act in a non-coordinated way, their joint actions lead to a suboptimal outcome, and make the common central bank face a trade-off between inflation and output gap stabilization at the union level.Monetary union, sticky prices, countercyclical policy, inflation differentials

Monetary Policy and Exchange Rate Volatility in a Small Open Economy

We lay out a small open economy version of the Calvo sticky price model, and show how the equilibrium dynamics can be reduced to a tractable canonical system in domestic inflation and the output gap. We employ this framework to analyze the macroeconomic implications of three alternative monetary policy regimes for the small open economy: domestic inflation targeting, CPI targeting and an exchange rate peg. We show that a key difference among these regimes lies in the relative amount of exchange rate volatility that they entail. We also discuss a special case for which domestic inflation targeting constitutes the optimal policy, and where a simple second order approximation to the utility of the representative consumer can be derived and used to evaluate the welfare losses associated with suboptimal regimes.

Optimal Monetary and Fiscal Policy in a Currency Union

We lay out a tractable model for fiscal and monetary policy analysis in a currency union, and analyze its implications for the optimal design of such policies. Monetary policy is conducted by a common central bank, which sets the interest rate for the union as a whole. Fiscal policy is implemented at the country level, through the choice of government spending level. The model incorporates country-specific shocks and nominal rigidities. Under our assumptions, the optimal monetary policy requires that inflation be stabilized at the union level. On the other hand, the relinquishment of an independent monetary policy, coupled with nominal price rigidities, generates a stabilization role for fiscal policy, one beyond the efficient provision of public goods. Interestingly, the stabilizing role for fiscal policy is shown to be desirable not only from the viewpoint of each individual country, but also from that of the union as a whole. In addition, our paper offers some insights on two aspects of policy design in currency unions: (i) the conditions for equilibrium determinacy and (ii) the effects of exogenous government spending variations.

Optimal Interest Rate Rules, Asset Prices and Credit Frictions

We study optimal monetary policy in two prototype economies with sticky prices and credit market frictions. In the first economy, credit frictions apply to the financing of the capital stock, generate acceleration in response to shocks and the "financial markup" (i.e., the premium on external funds) is countercyclical and negatively correlated with the asset price. In the second economy, credit frictions apply to the flow of investment, generate persistence, and the financial markup is procyclical and positively correlated with the asset price. We model monetary policy in terms of welfare-maximizing interest rate rules. The main finding of our analysis is that strict inflation stabilization is a robust optimal monetary policy prescription. The intuition is that, in both models, credit frictions work in the direction of dampening the cyclical behavior of inflation relative to its credit-frictionless level. Thus neither economy, despite yielding different inflation and investment dynamics, generates a trade-off between price and financial markup stabilization. A corollary of this result is that reacting to asset prices does not bear any independent welfare role in the conduct of monetary policy

Ramsey monetary policy and international relative prices

We analyze welfare maximizing monetary policy in a dynamic two-country model with price stickiness and imperfect competition. In this context, a typical terms of trade externality affects policy interaction between independent monetary authorities. Unlike the existing literature, we remain consistent to a public finance approach by an explicit consideration of all the distortions that are relevant to the Ramsey planner. This strategy entails two main advantages. First, it allows an accurate characterization of optimal policy in an economy that evolves around a steady-state which is not necessarily efficient. Second, it allows to describe a full range of alternative dynamic equilibria when price setters in both countries are completely forwardlooking and households’ preferences are not restricted. In this context, we study optimal policy both in the long-run and along a dynamic path, and we compare optimal commitment policy under Nash competition and under cooperation. By deriving a second order accurate solution to the policy functions, we also characterize the welfare gains from international policy cooperation. JEL Classification: E52, F41Cooperation, imperfect competition, Nash equilibrium, optimal monetary policy, Ramsey planner, sticky prices

Ramsey Monetary Policy and International Relative Prices

We analyze welfare maximizing monetary policy in a dynamic two-country model with price stickiness and imperfect competition. In this context, a typical terms of trade externality affects policy interaction between independent monetary authorities. Unlike the existing literature, we remain consistent to a public finance approach by an explicit consideration of all the distortions that are relevant to the Ramsey planner. This strategy entails two main advantages. First, it allows an accurate characterization of optimal policy in an economy that evolves around a steady-state which is not necessarily efficient. Second, it allows to describe a full range of alternative dynamic equilibria when price setters in both countries are completely forward-looking and households’ preferences are not restricted. In this context, we study optimal policy both in the long-run and along a dynamic path, and we compare optimal commitment policy under Nash competition and under cooperation. By deriving a second order accurate solution to the policy functions, we also characterize the welfare gains from international policy cooperation.