1,546 research outputs found
Free-Knot Spline Approximation of Stochastic Processes
We study optimal approximation of stochastic processes by polynomial splines
with free knots. The number of free knots is either a priori fixed or may
depend on the particular trajectory. For the -fold integrated Wiener process
as well as for scalar diffusion processes we determine the asymptotic behavior
of the average -distance to the splines spaces, as the (expected) number
of free knots tends to infinity.Comment: 23 page
A first step towards a direct inversion of the Lyman forest in QSO spectra
A method for the recovery of the real space line-of-sight mass density field
from Lyman absorption in QSO spectra is presented. The method makes use of a
Lucy-type algorithm for the recovery of the HI density. The matter density is
inferred from the HI density assuming that the absorption is due to a
photoionized intergalactic medium which traces the mass distribution as
suggested by recent numerical simulations. Redshift distortions are corrected
iteratively from a simultaneous estimate of the peculiar velocity. The method
is tested with mock spectra obtained from N-body simulations. The density field
is recovered reasonably well up to densities where the absorption features
become strongly saturated. The method is an excellent tool to study the density
probability distribution and clustering properties of the mass density in the
(mildly) non-linear regime. Combined with redshift surveys along QSO sightlines
the method will make it possible to relate the clustering of high-redshift
galaxies to the clustering of the underlying mass density. We further show that
accurate estimates for \Omega_{bar}h^2)^2 J^{-1} H(z)^{-1} and higher order
moments of the density probability function can be obtained despite the missing
high density tail of the density distribution if a parametric form for the
probability distribution of the mass density is assumed.Comment: 10 pages, 6 figure
Financial correlations at ultra-high frequency: theoretical models and empirical estimation
A detailed analysis of correlation between stock returns at high frequency is
compared with simple models of random walks. We focus in particular on the
dependence of correlations on time scales - the so-called Epps effect. This
provides a characterization of stochastic models of stock price returns which
is appropriate at very high frequency.Comment: 22 pages, 8 figures, 1 table, version to appear in EPJ
Universality of random matrix dynamics
We discuss the concept of width-to-spacing ratio which plays the central role
in the description of local spectral statistics of evolution operators in
multiplicative and additive stochastic processes for random matrices. We show
that the local spectral properties are highly universal and depend on a single
parameter being the width-to-spacing ratio. We discuss duality between the
kernel for Dysonian Brownian motion and the kernel for the Lyapunov matrix for
the product of Ginibre matrices.Comment: 15 pages, 3 figure
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