521,953 research outputs found
Non-linear estimation is easy
Non-linear state estimation and some related topics, like parametric
estimation, fault diagnosis, and perturbation attenuation, are tackled here via
a new methodology in numerical differentiation. The corresponding basic system
theoretic definitions and properties are presented within the framework of
differential algebra, which permits to handle system variables and their
derivatives of any order. Several academic examples and their computer
simulations, with on-line estimations, are illustrating our viewpoint
Quantum Circulant Preconditioner for Linear System of Equations
We consider the quantum linear solver for with the circulant
preconditioner . The main technique is the singular value estimation (SVE)
introduced in [I. Kerenidis and A. Prakash, Quantum recommendation system, in
ITCS 2017]. However, some modifications of SVE should be made to solve the
preconditioned linear system . Moreover, different from
the preconditioned linear system considered in [B. D. Clader, B. C. Jacobs, C.
R. Sprouse, Preconditioned quantum linear system algorithm, Phys. Rev. Lett.,
2013], the circulant preconditioner is easy to construct and can be directly
applied to general dense non-Hermitian cases. The time complexity depends on
the condition numbers of and , as well as the Frobenius norm
Structured variable selection and estimation
In linear regression problems with related predictors, it is desirable to do
variable selection and estimation by maintaining the hierarchical or structural
relationships among predictors. In this paper we propose non-negative garrote
methods that can naturally incorporate such relationships defined through
effect heredity principles or marginality principles. We show that the methods
are very easy to compute and enjoy nice theoretical properties. We also show
that the methods can be easily extended to deal with more general regression
problems such as generalized linear models. Simulations and real examples are
used to illustrate the merits of the proposed methods.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS254 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
On Marginal and Interaction Effects: The Case of Heckit and Two-Part Models
Interaction effects capture the impact of one explanatory variable x1 on the marginal effect of another explanatory variable x2. To explore interaction effects, so-called interaction terms x1x2 are typically included in estimation specifications. While in linear models the effect of a marginal change in the interaction term is equal to the interaction effect, this equality generally does not hold in non-linear specifications (AI, NORTON, 2003). This paper provides for a general derivation of marginal and interaction effects in both linear and non-linear models and calculates the formulae of the marginal and interaction effects resulting from HECKMAN's sample selection model as well as the Two-Part Model, two commonly employed censored regression models. Drawing on a survey of automobile use from Germany, we argue that while it is important to test for the significance of interaction effects, their size conveys limited substantive content. More meaningful, and also more easy to grasp, are the conditional marginal effects pertaining to two variables that are assumed to interact.Censored regression models, interaction terms
Estimation of elastic and viscous properties of the left ventricle based on annulus plane harmonic behavior
Assessment of left ventricular (LV) function
with an emphasis on contractility has been a challenge
in cardiac mechanics during the recent decades. The LV
function is usually described by the LV pressurevolume
(P-V) diagram. The standard P-V diagrams are
easy to interpret but difficult to obtain and require
invasive instrumentation for measuring the
corresponding volume and pressure data. In the present
study, we introduce a technique that can estimate the
viscoelastic properties of the LV based on harmonic
behavior of the ventricular chamber and it can be
applied non-invasively as well. The estimation technique
is based on modeling the actual long axis displacement
of the mitral annulus plane toward the cardiac base as a
linear damped oscillator with time-varying coefficients.
The time-varying parameters of the model were
estimated by a standard Recursive Linear Least
Squares (RLLS) technique. LV stiffness at end-systole
and end diastole was in the range of 61.86-136.00
dyne/g.cm and 1.25-21.02 dyne/g.cm, respectively. The
only input used in this model was the long axis
displacement of the annulus plane, which can also be
obtained non-invasively using tissue Doppler or MR
imaging
NICE: Non-linear Independent Components Estimation
We propose a deep learning framework for modeling complex high-dimensional
densities called Non-linear Independent Component Estimation (NICE). It is
based on the idea that a good representation is one in which the data has a
distribution that is easy to model. For this purpose, a non-linear
deterministic transformation of the data is learned that maps it to a latent
space so as to make the transformed data conform to a factorized distribution,
i.e., resulting in independent latent variables. We parametrize this
transformation so that computing the Jacobian determinant and inverse transform
is trivial, yet we maintain the ability to learn complex non-linear
transformations, via a composition of simple building blocks, each based on a
deep neural network. The training criterion is simply the exact log-likelihood,
which is tractable. Unbiased ancestral sampling is also easy. We show that this
approach yields good generative models on four image datasets and can be used
for inpainting.Comment: 11 pages and 2 pages Appendix, workshop paper at ICLR 201
Estimation of algal growth parameters from vertical primary production profiles
Phytoplankton maximum growth rate and the saturation light intensity, Is, can be estimated from vertical profiles of primary production by non-linear least-squares estimation. Solution through the normal equations leads to formulae which are relatively simple and easy to implement. The computation of confidence contours is demonstrated, and the results are contrasted to the confidence limits on the parameters individually. These can be quite misleading due to model non-linearity and correlation between parameter estimation.\ud
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The procedure has been applied to primary production data from Lake Balaton, a shallow lake in Hungary. The growth rate-temperature relation is analysed by separating the parameters into two groups characteristic for âwarmâ and âcoldâ water phytoplankton, respectively. A bell-shaped curve is found for âcoldâ water communities, with an optimum at about 7â9°C, whereas the âwarmâ water phytoplankton exhibits a strong exponential dependency in the temperature range of interest (up to 25°C). Is also appears to be related to temperature except for the âcoldâ water group, where Is is essentially constant. However, a roughly linear relation with considerably less scatter is obtained when Is is plotted directly versus day-averaged solar radiation. This apparent fast adaptation is attributed to the extremely short turnover time in Lake Balaton. Maximum growth rates of 10â20 dâ1 have been found for temperatures between 20 and 25°C. These results and a critical appraisal of available literature suggest that the common notion of maximum growth rates being in the order of 1â3 dâ1 needs revision, at least for lakes with relatively high summer temperatures
Forecasting exchange rates of major currencies with long maturity forward rates. Bruegel Working Paper | Issue 02 April 2020. Plus Annex in separate pdf
This paper presents unprecedented exchange rate forecasting results, based
upon a new model that approximates the gap between the fundamental
equilibrium exchange rate and the actual exchange rate with the longmaturity
forward exchange rate. The theoretical derivation of our forecasting
equation is consistent with the monetary model of exchange rates. Our
model outperforms the random walk in out-of-sample forecasting of twelve
major currency pairs over the short and long horizon forecasts for the 1990-
2020 period. The results are robust for all sub-periods, with the exception
of the years around the collapse of Lehman Brothers in September 2008.
Our results are robust to alternative model specifications, single equation
and panel estimation, recursive and rolling estimation, and alternate data
construction methods. The model performs better when the long-maturity
forward exchange rate is assumed to be stationary, as opposed to assuming
non-stationarity. The improvement in forecast accuracy from our model is
economically and statistically significant for almost all exchange-rate series.
The model is simple, linear, easy to replicate, and the data we use is available
in real time and not subject to revision
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