We analyze a Ramsey economy in which gross investment is constrained to be nonnegative. We prove the existence of a competitive equilibrium for the case in which utility need not be bounded from below and the Inada-type conditions need not hold. The analysis is carried out by means of a direct and technically standard approach. This direct approach allows us to obtain detailed results concerning properties of competitive equilibria, and is easily adapted for the analysis of analogous models often found in macroeconomics.

This paper analyzes the optimal inflation tax in economies with structural imperfections in labor, commodity, and currency markets. The Friedman rule is a classic result in economics that claims that the optimal monetary policy is to set a zero nominal interest rate. This Ramsey equilibrium is robust in a wide range of environments without imperfections in input, output, or financial markets. In many developing countries, however, a large fraction of activity takes place in the “informal” sector. Roughly speaking, the informal sector is the untaxed and unregulated market sometimes referred to as the underground economy. We obtain three results. First, we show that when structural imperfections such as an informal sector exist, the optimal inflation tax is positive. Second, we show that structural imperfections introduce an important asymmetry in the welfare cost function. Third, we provide quantitative results.

This paper presents an endogenous growth model in which the research activity is financed by intermediaries that are able to reduce the incidence of researcher's moral hazard. It is shown that financial activity is growth promoting because it increases research productivity. It is also found that a subsidy to the financial sector may have larger growth effects than a direct subsidy to research. Moreover, because of the presence of moral hazard, increasing the subsidy rate to R&D may reduce the growth rate. I show that there exists a negative relation between the financing of innovation and the process of capital accumulation. Concerning welfare, the presence of two externalities of opposite sign stemming from financial activity may cause the no-tax equilibrium to provide an inefficient level of financial services. Thus, policies oriented to balance the effects of the two externalities will be welfare improving.

It has been widely known that neoclassical growth models with sufficient increasing returns in production may feature indeterminacy. This note analytically shows that investment adjustment costs increase the required degree of increasing returns for indeterminacy to arise. Under empirically plausible levels of investment adjustment costs, we need an implausibly large degree of increasing returns to generate indeterminacy.

The paper studies the effects of an expansionary fiscal policy in a general equilibrium model of a small open economy. Households are assumed to possess habit-forming, endogenous rates of time preference. In response to fiscal shocks, the model generates cyclical endogenous persistence and procyclical time paths for consumption, employment, and investment, as well as a countercyclical path for the current account. Furthermore, fiscal shocks are shown to have positive long-run effects on output and negative long-run effects on consumption.

This paper is helpful for understanding interactive-agent economies. It presents a user-friendly framework for exploring the implications of economic interaction, and demonstrates its wide applicability. Agents repeatedly face binary choices and receive i.i.d. shocks; payoffs depend upon one's own action and shocks, as well as upon the actions of a subset of other agents. Simulations explore how properties change as the number of agents, the number of neighbors, and the degree of interaction change. Key results in this framework include the following: The law of large numbers can readily be postponed or defeated, stationarity and ergodicity are trivial to deduce, any equilibrium distribution may be attained in “globally interactive” economies, continuous- and discrete-time analogues generally behave very similarly, dynamics can be sensitive to details of the interaction structure (implying that popular mean-field approximations are not always appropriate), and substantial persistence is typical.

The objective of this book is to provide “a systematic theory of endogenous business fluctuations and growth with a hierarchical structure of integrated macro-dynamical models” (p. 372). The starting point is Tobin's neoclassical model of monetary growth, and successive chapters show how Tobin's model can be extended in various “realistic” directions while preserving the relevant adding-up and balance-sheet constraints of a macro model. The work reported here is squarely in an ongoing European theoretical tradition that eschews the stochastic, representative-agent, approach to macroeconomic modeling. Absent stochastic disturbances, the authors provide a qualitative analysis of dynamic behavior for a variety of closed-economy models—a variety that, as the authors themselves point out, is closely related to three prototype models studied in Part I of Sargent's 1977 book, Macroeconomic Theory.