More on A Statistical Analysis of Log-Periodic Precursors to Financial Crashes

We respond to Sornette and Johansen's criticisms of our findings regarding log-periodic precursors to financial crashes. Included in this paper are discussions of the Sornette-Johansen theoretical paradigm, traditional methods of identifying log-periodic precursors, the behavior of the first differences of a log-periodic price series, and the distribution of drawdowns for a securities price.Comment: 12 LaTex pages, no figure

"Thermometers" of Speculative Frenzy

Establishing unambiguously the existence of speculative bubbles is an on-going controversy complicated by the need of defining a model of fundamental prices. Here, we present a novel empirical method which bypasses all the difficulties of the previous approaches by monitoring external indicators of an anomalously growing interest in the public at times of bubbles. From the definition of a bubble as a self-fulfilling reinforcing price change, we identify indicators of a possible self-reinforcing imitation between agents in the market. We show that during the build-up phase of a bubble, there is a growing interest in the public for the commodity in question, whether it consists in stocks, diamonds or coins. That interest can be estimated through different indicators: increase in the number of books published on the topic, increase in the subscriptions to specialized journals. Moreover, the well-known empirical rule according to which the volume of sales is growing during a bull market finds a natural interpretation in this framework: sales increases in fact reveal and pinpoint the progress of the bubble's diffusion throughout society. We also present a simple model of rational expectation which maps exactly onto the Ising model on a random graph. The indicators are then interpreted as ``thermometers'', measuring the balance between idiosyncratic information (noise temperature) and imitation (coupling) strength. In this context, bubbles are interpreted as low or critical temperature phases, where the imitation strength carries market prices up essentially independently of fundamentals. Contrary to the naive conception of a bubble and a crash as times of disorder, on the contrary, we show that bubbles and crashes are times where the concensus is too strong.Comment: 15 pages + 10 figure

Peso Problems, Bubbles, and Risk in the Empirical Assessment of Exchange-Rate Behavior

One of the most puzzling aspects of the post-1973 floating exchange rate system has been the apparently inefficient predictive performance of forward exchange rates. This paper explores some aspects of each of three leading explanations of forward-rate behavior. The paper first develops a simple rational-expectations model of the "peso problem" that generates some key empirical regularities of the foreign exchange market: seemingly predictable and conditionally heteroskedastic forward forecast errors, along with possible directional misprediction by the forward premium. The implications of bubbles for tests of forward-rate predictive efficiency are discussed next. It is argued that the existence of bubbles is extremely difficult (if not impossible) to establish empirically. Even though some types of bubble would distort standard tests on the relation between spot and forward exchange rates, it seems unlikely that there bubbles have been an important factor. Finally, the paper examines foreign-exchange asset pricing under risk aversion and suggests that a convincing account of forward-rate behavior should also help explain the results found in testing other asset-pricing theories, such as the expectations theory of the interest-rate term structure.

Bubble-free interest-rate rules.

This paper designs, for a broad class of rational-expectations dynamic stochastic general-equilibrium models, interest-rate rules which not only ensure the local determinacy of the targeted equilibrium within the neighbourhood of the targeted steady state, but also prevent the economy from gradually leaving this neighbourhood. We show that in most models these interest-rate rules are necessarily forward-looking (i.e. make necessarily the interest rate conditional on the private agents' expectations), while in all models non-forward-looking interest-rate rules exist which ensure only the local determinacy of the targeted equilibrium. We also discuss the robustness of the effectiveness of these rules to departures from various assumptions and show in particular that they can still be effective when the central bank has imperfect knowledge of the model's structural parameters. We finally argue that such rules could also serve as a useful guide in the reflections on the best monetary policy reaction to perceived asset-price bubbles or exchange-rate misalignments.DSGE models ; Interest-rate rules ; Local determinacy ; Global determinacy ; Rational bubbles

Evaluating critical bits in arithmetic operations due to timing violations

Various error models are being used in simulation of voltage-scaled arithmetic units to examine application-level tolerance of timing violations. The selection of an error model needs further consideration, as differences in error models drastically affect the performance of the application. Specifically, floating point arithmetic units (FPUs) have architectural characteristics that characterize its behavior. We examine the architecture of FPUs and design a new error model, which we call Critical Bit. We run selected benchmark applications with Critical Bit and other widely used error injection models to demonstrate the differences

Credit Termination and the Technology Bubbles

We study the role of firms' credit histories in a business cycle model. Loans are dynamic contracts between banks and firms, and credit terminations are used as an incentive device. Banks deny future loans to an entrepreneur according to his credit histories in order to affect his choice of project ex ante. This will generate fluctuations from technology shocks to the riskiness of different types of projects as occurred during the technology bubbles. The model is used to explain the boom-and-bust of the dot-com bubble, one leading example of technology bubbles in the economy, in the late 1990s.credit terminations; technology bubbles