28,176 research outputs found
RANDOM WALKS AND FRACTAL STRUCTURES IN AGRICULTURAL COMMODITY FUTURES PRICES
This paper investigates whether the assumption of Brownian motion often used to describe commodity price movements is satisfied. Using historical data from 17 commodity futures contracts specific tests of fractional and ordinary Brownian motion are conducted. The analyses are conducted under the null hypothesis of ordinary Brownian motion against the alternative of persistent or ergodic fractional Brownian motion. Tests for fractional Brownian motion are based on a variance ratio test and compared with conventional R-S analyses. However, standard errors based on Monte Carlo simulations are quite high, meaning that the acceptance region for the null hypothesis is large. The results indicate that for the most part, the null hypothesis of ordinary Brownian motion cannot be rejected for 14 of 17 series. The three series that did not satisfy the tests were rejected because they violated the stationarity property of the random walk hypothesis.Demand and Price Analysis, Marketing,
Efficient Management of Short-Lived Data
Motivated by the increasing prominence of loosely-coupled systems, such as
mobile and sensor networks, which are characterised by intermittent
connectivity and volatile data, we study the tagging of data with so-called
expiration times. More specifically, when data are inserted into a database,
they may be tagged with time values indicating when they expire, i.e., when
they are regarded as stale or invalid and thus are no longer considered part of
the database. In a number of applications, expiration times are known and can
be assigned at insertion time. We present data structures and algorithms for
online management of data tagged with expiration times. The algorithms are
based on fully functional, persistent treaps, which are a combination of binary
search trees with respect to a primary attribute and heaps with respect to a
secondary attribute. The primary attribute implements primary keys, and the
secondary attribute stores expiration times in a minimum heap, thus keeping a
priority queue of tuples to expire. A detailed and comprehensive experimental
study demonstrates the well-behavedness and scalability of the approach as well
as its efficiency with respect to a number of competitors.Comment: switched to TimeCenter latex styl
AMaÏoSâAbstract Machine for Xcerpt
Web query languages promise convenient and efficient access
to Web data such as XML, RDF, or Topic Maps. Xcerpt is one such Web
query language with strong emphasis on novel high-level constructs for
effective and convenient query authoring, particularly tailored to versatile
access to data in different Web formats such as XML or RDF.
However, so far it lacks an efficient implementation to supplement the
convenient language features. AMaÏoS is an abstract machine implementation
for Xcerpt that aims at efficiency and ease of deployment. It
strictly separates compilation and execution of queries: Queries are compiled
once to abstract machine code that consists in (1) a code segment
with instructions for evaluating each rule and (2) a hint segment that
provides the abstract machine with optimization hints derived by the
query compilation. This article summarizes the motivation and principles
behind AMaÏoS and discusses how its current architecture realizes
these principles
How sensitive are equilibrium pricing models to real-world distortions?
In both finance and economics, quantitative models are usually studied as
isolated mathematical objects --- most often defined by very strong simplifying
assumptions concerning rationality, efficiency and the existence of
disequilibrium adjustment mechanisms. This raises the important question of how
sensitive such models might be to real-world effects that violate the
assumptions. We show how the consequences of rational behavior caused by
perverse incentives, as well as various irrational tendencies identified by
behavioral economists, can be systematically and consistently introduced into
an agent-based model for a financial asset. This generates a class of models
which, in the special case where such effects are absent, reduces to geometric
Brownian motion --- the usual equilibrium pricing model. Thus we are able to
numerically perturb a widely-used equilibrium pricing model market and
investigate its stability. The magnitude of such perturbations in real markets
can be estimated and the simulations imply that this is far outside the
stability region of the equilibrium solution, which is no longer observed.
Indeed the price fluctuations generated by endogenous dynamics, are in good
general agreement with the excess kurtosis and heteroskedasticity of actual
asset prices. The methodology is presented within the context of a financial
market. However, there are close links to concepts and theories from both
micro- and macro-economics including rational expectations, Soros' theory of
reflexivity, and Minsky's theory of financial instability
Portfolio Optimization and Long-Term Dependence
Whilst emphasis has been given to short-term dependence of financial returns, long-term dependence remains overlooked. Despite financial literature provides evidence of long-termâs memory existence, serial-independence assumption prevails. This documentâs long-term dependence assessment relies on rescaled range analysis (R/S), a popular and robust methodology designed for Geophysics but extensively used in financial literature. Results correspond to most of the previous evidence of significant long-term dependence, particularly for small and illiquid markets, where persistence is its most common kind. Persistence conveys that the range of possible future values of the variable will be wider than the range of purely random and independent variables. Ahead of R/S financial literature, authors estimate an adjusted Hurst exponent in order to properly estimate the covariance matrix at higher investment horizons, avoiding the traditional -independence reliant- square-root-of-time rule. Ignoring long-term dependence within the mean-variance portfolio optimization results in concealed risk taking; conversely, by adjusting for long-term dependence the weight of high (low) persistence risk factors decreases (increases) as the investment horizon widens. This alleviates some well-known shortcomings of conventional portfolio optimization for long-term investors (e.g. central banks, pension funds and sovereign wealth managers), such as excessive risk taking in long-term portfolios, extreme weights, home bias, and reluctance to hold foreign currency-denominated assets.Portfolio optimization, Hurst exponent, long-term dependence, biased random walk, rescaled range analysis. Classification JEL: G11, G32, G20, C14.
A self-adjusted Monte Carlo simulation as model of financial markets with central regulation
Properties of the self-adjusted Monte Carlo algorithm applied to 2d Ising
ferromagnet are studied numerically. The endogenous feedback form expressed in
terms of the instant running averages is suggested in order to generate a
biased random walk of the temperature that converges to criticality without an
external tuning. The robustness of a stationary regime with respect to partial
accessibility of the information is demonstrated. Several statistical and
scaling aspects have been identified which allow to establish an alternative
spin lattice model of the financial market. It turns out that our model alike
model suggested by S. Bornholdt, Int. J. Mod. Phys. C {\bf 12} (2001) 667, may
be described by L\'evy-type stationary distribution of feedback variations with
unique exponent . However, the differences reflected by
Hurst exponents suggest that resemblances between the studied models seem to be
nontrivial.Comment: 19 pages, 9 figures, 30 reference
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