The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Paresh Kumar Narayan - One of the best experts on this subject based on the ideXlab platform.
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are bilateral real exchange rates stationary evidence from Lagrange Multiplier unit root tests for india
Social Science Research Network, 2012Co-Authors: Paresh Kumar NarayanAbstract:The paper examines the stationarity of India's real exchange rate vis-a-vis 16 of its major trading partner countries for the period 1960-2000. Application of the conventional ADF unit root test, the Lagrange Multiplier (LM) unit root test with one structural break, and the LM unit root test with two structural breaks provides evidence that India's exchange rate vis-a-vis 15 out of 16 countries is stationary, implying support for purchasing power parity.
Mark C Strazicich - One of the best experts on this subject based on the ideXlab platform.
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minimum Lagrange Multiplier unit root test with two structural breaks
The Review of Economics and Statistics, 2003Co-Authors: Junsoo Lee, Mark C StrazicichAbstract:The endogenous two-break unit root test of Lumsdaine and Papell is derived assuming no structural breaks under the null. Thus, rejection of the null does not necessarily imply rejection of a unit root per se, but may imply rejection of a unit root without break. Similarly, the alternative does not necessarily imply trend stationarity with breaks, but may indicate a unit root with breaks. In this paper, we propose an endogenous two-break Lagrange Multiplier unit root test that allows for breaks under both the null and alternative hypotheses. As a result, rejection of the null unambiguously implies trend stationarity.
Jacques Periaux - One of the best experts on this subject based on the ideXlab platform.
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distributed Lagrange Multiplier methods for incompressible viscous flow around moving rigid bodies
Computer Methods in Applied Mechanics and Engineering, 1998Co-Authors: Roland Glowinski, Tsorngwhay Pan, Jacques PeriauxAbstract:Abstract In this article we discuss the application of a distributed Lagrange Multiplier based fictitious domain method to the numerical simulation of incompressible viscous flow modelled by the Navier-Stokes equations around moving bodies, we suppose the rigid bodies motion known a priori. The solution method combines finite element approximations, time discretization by operator splitting and conjugate gradient algorithms for the solution of the linearly constrained quadratic minimization problems coming from the splitting method. Numerical experiment results for two-dimensional flow around a moving disk are presented.
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a Lagrange Multiplier fictitious domain method for the dirichlet problem generalization to some flow problems
Japan Journal of Industrial and Applied Mathematics, 1995Co-Authors: Roland Glowinski, Jacques PeriauxAbstract:In this article we discuss the solution of the Dirichlet problem for a class of elliptic operators by a Lagrange Multiplier/fictitious domain method. This approach allows the use of regular grids and therefore of fast specialized solvers for problems on complicated geometries; the resulting saddle-point system can be solved by an Uzawa/conjugate gradient algorithm. The resulting methodology is applied to the solution of some flow problems, including external incompressible viscous flow modelled by Navier-Stokes equations.
Sergei D Odintsov - One of the best experts on this subject based on the ideXlab platform.
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viable non singular cosmic bounce in holonomy improved f r gravity endowed with a Lagrange Multiplier
European Physical Journal C, 2020Co-Authors: E Elizalde, Sergei D Odintsov, Tanmoy PaulAbstract:Matter and quasi-matter bounce scenarios are studied for an F(R) gravity model with holonomy corrections and a Lagrange Multiplier, with a scale factor $$a(t) = \left( a_0t^2 + 1 \right) ^n$$, where the Hubble parameter squared has a linear and a quadratic dependence on the effective energy density. Provided $$n < 1/2$$, it is shown that the primordial curvature perturbations are generated deeply into the contracting era, at large negative time, which makes the low-curvature limit a good approximation for calculating the perturbation power spectrum. Moreover, it is shown that, for n within this range, the obtained cosmological quantities are fully compatible with the Planck constraints, and that the “low curvature limit” comes as a viable approximation to calculate the power spectra of both scalar and tensor perturbations. Using reconstruction techniques for F(R) gravity with the Lagrange Multiplier, the precise form of the effective F(R) gravity is found, from which one determines the power spectra of scalar and tensor perturbations in such bouncing scenario. Correspondingly, the spectral index for curvature perturbations and the tensor to scalar ratio are obtained, and these values are successfully confronted with the latest Planck observations. Further, it is shown that both the weak and the null energy conditions are satisfied, thanks to the holonomy corrections performed in the theory–which are then proven to be necessary for achieving this goal. In fact, when approaching the bouncing era, the holonomy corrections become significant and play a crucial role in order to restore the energy conditions. Summing up, a cosmological bouncing scenario with the scale factor above and fulfilling the energy conditions can be adequately described by the F(R) model with a Lagrange Multiplier and holonomy corrections, which prove to be very important.
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nonsingular bounce cosmology from Lagrange Multiplier f r gravity
Physical Review D, 2019Co-Authors: Shinichi Nojiri, Sergei D Odintsov, V K Oikonomou, Tanmoy PaulAbstract:In this work, we study nonsingular bounce cosmology in the context of the Lagrange Multiplier generalized $F(R)$ gravity theory of gravity. We specify our study by using a specific variant form of the well-known matter bounce cosmology, with scale factor $a(t)={({a}_{0}{t}^{2}+1)}^{n}$, and we demonstrate that for $nl1/2$, the primordial curvature perturbations are generated deeply in the contraction era. Particularly, we show explicitly that the perturbation modes exit the horizon at a large negative time during the contraction era, which in turn makes the ``low-curvature'' regime, the era for which the calculations of observational indices related to the primordial power spectrum can be considered reliable. Using the reconstruction techniques for the Lagrange Multiplier $F(R)$ gravity, we construct the form of effective $F(R)$ gravity that can realize such a cosmological evolution, and we determine the power spectrum of the primordial curvature perturbations. Accordingly, we calculate the spectral index of the primordial curvature perturbations and the tensor-to-scalar ratio, and we confront these with the latest observational data. We also address the issue of stability of the primordial metric perturbations, and to this end, we determine the form of $F(R)$ which realizes the nonsingular cosmology for the whole range of cosmic time $\ensuremath{-}\ensuremath{\infty}ltl\ensuremath{\infty}$, by solving the Friedmann equations without the ``low-curvature'' approximation. This study is performed numerically though, due to the high complexity of the resulting differential equations. By using this numerical solution, we show that the stability is achieved for the same range of values of the free parameters that guarantee the phenomenological viability of the model. We also investigate the energy conditions in the present context. The phenomenology of the no-singular bounce is also studied in the context of a standard $F(R)$ gravity. We find that the results obtained in the Lagrange Multiplier $F(R)$ gravity model have differences in comparison to the standard $F(R)$ gravity model, where the observable indices are not simultaneously compatible with the latest Planck results, and also the standard $F(R)$ gravity model is plagued with instabilities of the perturbation. These facts clearly justify the importance of the Lagrange Multiplier field in making the observational indices compatible with the Planck data and also in removing the instabilities of the metric perturbations. Thereby, the bounce with the aforementioned scale factor is adequately described by the Lagrange Multiplier $F(R)$ gravity, in comparison to the standard $F(R)$ model.
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ghost free f r gravity with Lagrange Multiplier constraint
Physics Letters B, 2017Co-Authors: Shinichi Nojiri, Sergei D Odintsov, V K OikonomouAbstract:Abstract We propose two new versions of ghost-free generalized F ( R ) gravity with Lagrange Multiplier constraint. The first version of such theory for a particular degenerate choice of the Lagrange Multiplier, corresponds to mimetic F ( R ) gravity. The second version of such theory is just the Jordan frame description of mimetic gravity with potential. As we demonstrate, it is possible to realize several cosmological scenarios in such theory. In particular, de Sitter solutions may also be found.
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modified gauss bonnet gravity with Lagrange Multiplier constraint as mimetic theory
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Artyom V Astashenok, Sergei D Odintsov, V K OikonomouAbstract:In this paper we propose and extensively study mimetic $f({\cal G})$ modified gravity models, with various scenarios of cosmological evolution, with or without extra matter fluids. The easiest formulation is based on the use of Lagrange Multiplier constraint. In certain versions of this theory, it is possible to realize accelerated expansion of the Universe or even unified evolution which includes inflation with dark energy, and at the same time in the same theoretical framework, dark matter is described by the theory. This is achieved by the re-parametrization of the metric tensor, which introduces a new degree of freedom in the cosmological equations and leads to appearance of the mimetic "dark matter" component. In the context of mimetic $f({\cal G})$ theory, we also provide some quite general reconstruction schemes, which enable us to find which $f({\cal G})$ gravity generates a specific cosmological evolution. In addition, we also provide the general reconstruction technique for Lagrange Multiplier $f({\cal G})$ gravity. All our results are accompanied by illustrative examples, with special emphasis on bouncing cosmologies.
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covariant Lagrange Multiplier constrained higher derivative gravity with scalar projectors
Physics Letters B, 2011Co-Authors: Josef Klusoň, S Nojiri, Sergei D OdintsovAbstract:We formulate higher derivative gravity with Lagrange Multiplier constraint and scalar projectors. Its gauge-fixed formulation as well as vector fields formulation is developed and corresponding spontaneous Lorentz symmetry breaking is investigated. We show that the only propagating mode is higher derivative graviton while scalar and vector modes do not propagate. Despite to higher derivatives structure of the action, its first FRW equation is the first order differential equation which admits the inflationary universe solution.
Junsoo Lee - One of the best experts on this subject based on the ideXlab platform.
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minimum Lagrange Multiplier unit root test with two structural breaks
The Review of Economics and Statistics, 2003Co-Authors: Junsoo Lee, Mark C StrazicichAbstract:The endogenous two-break unit root test of Lumsdaine and Papell is derived assuming no structural breaks under the null. Thus, rejection of the null does not necessarily imply rejection of a unit root per se, but may imply rejection of a unit root without break. Similarly, the alternative does not necessarily imply trend stationarity with breaks, but may indicate a unit root with breaks. In this paper, we propose an endogenous two-break Lagrange Multiplier unit root test that allows for breaks under both the null and alternative hypotheses. As a result, rejection of the null unambiguously implies trend stationarity.
