Optimal Interest Rate Policy in a Small Open Economy

Using an optimizing model we derive the optimal monetary and exchange rate policy for a small stochastic open economy with imperfect competition and short run price rigidity. The optimal monetary policy has an exact closed-form solution and is obtained using the utility function of the representative home agent as welfare criterion. The optimal policy depends on the source of stochastic disturbances affecting the economy, much as in the literature pioneered by Poole (1970). Optimal monetary policy reacts to domestic and foreign disturbances. If the intertemporal elasticity of substitution in consumption is less than one, as is likely to be the case empirically, the optimal exchange rate policy implies a dirty float: interest rate shocks from abroad are met partially by adjusting home interest rates, and partially by allowing the exchange rate to move. This optimal pattern may help rationalize the observed fear of floating.

On Conservative and Monotone One-dimensional Cellular Automata and Their Particle Representation

Number-conserving (or {\em conservative}) cellular automata have been used in several contexts, in particular traffic models, where it is natural to think about them as systems of interacting particles. In this article we consider several issues concerning one-dimensional cellular automata which are conservative, monotone (specially ``non-increasing''), or that allow a weaker kind of conservative dynamics. We introduce a formalism of ``particle automata'', and discuss several properties that they may exhibit, some of which, like anticipation and momentum preservation, happen to be intrinsic to the conservative CA they represent. For monotone CA we give a characterization, and then show that they too are equivalent to the corresponding class of particle automata. Finally, we show how to determine, for a given CA and a given integer $b$, whether its states admit a $b$-neighborhood-dependent relabelling whose sum is conserved by the CA iteration; this can be used to uncover conservative principles and particle-like behavior underlying the dynamics of some CA. Complements at {\tt http://www.dim.uchile.cl/\verb' 'anmoreir/ncca}Comment: 38 pages, 2 figures. To appear in Theo. Comp. Sc. Several changes throughout the text; major change in section 4.

Complexity of Langton's Ant

The virtual ant introduced by C. Langton has an interesting behavior, which has been studied in several contexts. Here we give a construction to calculate any boolean circuit with the trajectory of a single ant. This proves the P-hardness of the system and implies, through the simulation of one dimensional cellular automata and Turing machines, the universality of the ant and the undecidability of some problems associated to it.Comment: 8 pages, 9 figures. Complements at http://www.dim.uchile.cl/~agajardo/langto

The supercover of an m-flat is a discrete analytical object

International audienc

Digital Analytical Geometry: How do I define a digital analytical object?

International audienceThis paper is meant as a short survey on analytically de-ned digital geometric objects. We will start by giving some elements on digitizations and its relations to continuous geometry. We will then explain how, from simple assumptions about properties a digital object should have, one can build mathematical sound digital objects. We will end with open problems and challenges for the future

Discrete linear objects in dimension n: the standard model

International audienceA new analytical description model, called the standard model, for the discretization of Euclidean linear objects (point, m-flat, m-simplex) in dimension n is proposed. The objects are defined analytically by inequalities. This allows a global definition independent of the number of discrete points. A method is provided to compute the analytical description for a given linear object. A discrete standard model has many properties in common with the supercover model from which it derives. However, contrary to supercover objects, a standard object does not have bubbles. A standard object is (n-1)-connected, tunnel-free and bubble-free. The standard model is geometrically consistent. The standard model is well suited for modelling applications

A generalized preimage for the digital analytical hyperplane recognition

International audienceA new digital hyperplane recognition method is presented. This algorithm allows the recognition of digital analytical hyperplanes, such as Naive, Standard and Supercover ones. The principle is to incrementally compute in a dual space the generalized preimage of the ball set corresponding to a given hypervoxel set according to the chosen digitization model. Each point in this preimage corresponds to a Euclidean hyperplane the digitization of which contains all given hypervoxels. An advantage of the generalized preimage is that it does not depend on the hypervoxel locations. Moreover, the proposed recognition algorithm does not require the hypervoxels to be connected or ordered in any way

Two discrete-continuous operations based on the scaling transform

International audienceIn this paper we study the relationship between the Euclidean and the discrete world thru two operations based on the Euclidean scaling function: the discrete smooth scaling and the discrete based geometrical simplification

Discrete-Euclidean operations

International audienceIn this paper we study the relationship between the Euclidean and the discrete space. We study discrete operations based on Euclidean functions: the discrete smooth scaling and the discrete-continuous rotation. Conversely, we study Euclidean oper- ations based on discrete functions: the discrete based simplification, the Euclidean- discrete union and the Euclidean-discrete co-refinement. These operations operate partly in the discrete and partly in the continuous space. Especially for the discrete smooth scaling operation, we provide error bounds when different such operations are chained