98,879 research outputs found
Multivariate transient price impact and matrix-valued positive definite functions
We consider a model for linear transient price impact for multiple assets
that takes cross-asset impact into account. Our main goal is to single out
properties that need to be imposed on the decay kernel so that the model admits
well-behaved optimal trade execution strategies. We first show that the
existence of such strategies is guaranteed by assuming that the decay kernel
corresponds to a matrix-valued positive definite function. An example
illustrates, however, that positive definiteness alone does not guarantee that
optimal strategies are well-behaved. Building on previous results from the
one-dimensional case, we investigate a class of nonincreasing, nonnegative and
convex decay kernels with values in the symmetric matrices. We show
that these decay kernels are always positive definite and characterize when
they are even strictly positive definite, a result that may be of independent
interest. Optimal strategies for kernels from this class are well-behaved when
one requires that the decay kernel is also commuting. We show how such decay
kernels can be constructed by means of matrix functions and provide a number of
examples. In particular we completely solve the case of matrix exponential
decay
Heat kernel measures on random surfaces
The heat kernel on the symmetric space of positive definite Hermitian
matrices is used to endow the spaces of Bergman metrics of degree k on a
Riemann surface M with a family of probability measures depending on a choice
of the background metric. Under a certain matrix-metric correspondence, each
positive definite Hermitian matrix corresponds to a Kahler metric on M. The one
and two point functions of the random metric are calculated in a variety of
limits as k and t tend to infinity. In the limit when the time t goes to
infinity the fluctuations of the random metric around the background metric are
the same as the fluctuations of random zeros of holomorphic sections. This is
due to the fact that the random zeros form the boundary of the space of Bergman
metrics.Comment: 20 pages, v2: minor correction
Permanental Vectors
A permanental vector is a generalization of a vector with components that are
squares of the components of a Gaussian vector, in the sense that the matrix
that appears in the Laplace transform of the vector of Gaussian squares is not
required to be either symmetric or positive definite. In addition the power of
the determinant in the Laplace transform of the vector of Gaussian squares,
which is -1/2, is allowed to be any number less than zero.
It was not at all clear what vectors are permanental vectors. In this paper
we characterize all permanental vectors in and give applications to
permanental vectors in and to the study of permanental processes
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