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Complexity and Error Analysis of Numerical Methods for Wireless Channels, SDE, Random Variables and Quantum Mechanics
KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA (closed 2012-06-30).
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis consists of the four papers which consider different aspects of stochastic process modeling, error analysis, and minimization of computational cost.

     In Paper I, we construct a Multipath Fading Channel (MFC) model for wireless channels with noise introduced through scatterers flipping on and off. By coarse graining the MFC model a Gaussian process channel model is developed. Complexity and accuracy comparisons of the models are conducted.

     In Paper II, we generalize a multilevel Forward Euler Monte Carlo method introduced by Mike Giles for the approximation of expected values depending on solutions of Ito stochastic differential equations. Giles' work proposed and analyzed a Forward Euler Multilevel Monte Carlo (MLMC) method based on realizations on a hierarchy of uniform time discretizations and a coarse graining based control variates idea to reduce the computational cost required by a standard single level Forward Euler Monte Carlo method. This work is an extension of Giles' MLMC method from uniform to adaptive time grids. It has the same improvement in computational cost and is applicable to a larger set of problems.

     In paper III, we consider the problem to estimate the mean of a random variable by a sequential stopping rule Monte Carlo method. The performance of a typical second moment based sequential stopping rule is shown to be unreliable both by numerical examples and by analytical arguments. Based on analysis and approximation of error bounds we construct a higher moment based stopping rule which performs more reliably.

     In paper IV, Born-Oppenheimer dynamics is shown to provide an accurate approximation of time-independent Schrödinger observables for a molecular system with an electron spectral gap, in the limit of large ratio of nuclei and electron masses, without assuming that the nuclei are localized to vanishing domains. The derivation, based on a Hamiltonian system interpretation of the Schrödinger equation and stability of the corresponding hitting time Hamilton-Jacobi equation for non ergodic dynamics, bypasses the usual separation of nuclei and electron wave functions, includes caustic states and gives a different perspective on the Born-Oppenheimer approximation, Schrödinger Hamiltonian systems and numerical simulation in molecular dynamics modeling at constant energy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , vii, 65 p.
Series
Trita-CSC-A, ISSN 1653-5723 ; 2012:06
Keyword [en]
Wireless Channels; SDE; Monte Carlo Methods, Molecular Dynamics, Quantum Mechanics
National Category
Computational Mathematics Probability Theory and Statistics
Identifiers
URN: urn:nbn:se:kth:diva-94150ISBN: 978-91-7501-350-3 (print)OAI: oai:DiVA.org:kth-94150DiVA: diva2:525531
Public defence
2012-05-30, F3, Lindstedtsvägen 26, Kungliga Tekniska högskolan, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20120508

Available from: 2012-05-08 Created: 2012-05-08 Last updated: 2013-04-09Bibliographically approved
List of papers
1. Gaussian Coarse Graining of a Master Equation Extension of Clarke's Model
Open this publication in new window or tab >>Gaussian Coarse Graining of a Master Equation Extension of Clarke's Model
2012 (English)Report (Other academic) [Artistic work]
Abstract [en]

We study the error and computational cost of generating outputsignal realizations for the channel model of a moving receiver in a scatteringenvironment, as in Clarke’s model, with the extension that scatterers randomlyflip on and off. At micro scale, the channel is modeled by a Multipath FadingChannel (MFC) model, and by coarse graining the micro scale model we derivea macro scale Gaussian process model. Four algorithms are presented for gen-erating stochastic signal realizations, one for the MFC model and three for theGaussian process model. A computational cost comparison of the presentedalgorithms indicates that Gaussian process algorithms generate signal realiza-tions more efficiently than the MFC algorithm does. Numerical examples ofgenerating signal realizations in time independent and time dependent scatter-ing environments are given, and the problem of estimating model parametersfrom real life signal measurements is also studied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 30 p.
Series
Trita-NA, ISSN 0348-2952 ; 2012:5
Keyword
Wireless channel modeling; signal theory; master equations; Gaussian processes
National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:kth:diva-94105 (URN)
Note
Funded by Centre for Industrial and Applied Mathematics (CIAM). QC 20120508Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2012-05-08Bibliographically approved
2. Implementation and Analysis of an Adaptive Multilevel Monte Carlo Algorithm
Open this publication in new window or tab >>Implementation and Analysis of an Adaptive Multilevel Monte Carlo Algorithm
2012 (English)Report (Other academic)
Abstract [en]

This work generalizes a multilevel Monte Carlo (MLMC) method in-troduced in [7] for the approximation of expected values of functions depending on the solution to an Ito stochastic differential equation. The work [7] proposed and analyzed a forward Euler MLMC method based on a hierarchy of uniform time discretizations and control variates to reduce the computational effort required by a standard, single level, forward Euler Monte Carlo method from O( TOL^(−3) ) to O( TOL^(−2) log( TOL^(−1))^2 ) for a meansquare error of size 2 . This work uses instead a hierarchy of adaptivelyrefined, non uniform, time discretizations, generated by an adaptive algo-rithm introduced in [20, 19, 5]. Given a prescribed accuracy TOL in theweak error, this adaptive algorithm generates time discretizations basedon a posteriori expansions of the weak error first developed in [24]. Atheoretical analysis gives results on the stopping, the accuracy, and thecomplexity of the resulting adaptive MLMC algorithm. In particular, it isshown that: the adaptive refinements stop after a finite number of steps;the probability of the error being smaller than TOL is under certain as-sumptions controlled by a given confidence parameter, asymptotically asTOL → 0; the complexity is essentially the expected for MLMC methods,but with better control of the constant factors. We also show that themultilevel estimator is asymptotically normal using the Lindeberg-FellerCentral Limit Theorem. These theoretical results are based on previouslydeveloped single level estimates, and results on Monte Carlo stoppingfrom [3]. Our numerical tests include cases, one with singular drift andone with stopped diffusion, where the complexity of uniform single levelmethod is O TOL−4 . In both these cases the results confirm the theoryby exhibiting savings in the computational cost to achieve an accuracy of O(TOL), from O( TOL^(−3) )for the adaptive single level algorithm toessentially O( TOL^(−2) log(TOL−1)^2 ) for the adaptive MLMC.

Publisher
57 p.
Series
TRITA-NA, ISSN 0348-2952 ; 2012:6
Keyword
computational finance; Monte Carlo; multi-level; adaptivity; weak approximation
National Category
Probability Theory and Statistics Computer Engineering
Identifiers
urn:nbn:se:kth:diva-94108 (URN)
Note

QC 20120508

Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2016-12-22Bibliographically approved
3. On non-asymptotic optimal stopping criteria in Monte Carlo simulations
Open this publication in new window or tab >>On non-asymptotic optimal stopping criteria in Monte Carlo simulations
2012 (English)Report (Other academic)
Abstract [en]

We consider the setting of estimating the mean of a random variable by a sequential stopping rule Monte Carlo (MC) method. The performance of a typical second moment based sequential stopping rule MC method is shown to be unreliable in such settings both by numerical examples and through analysis. By analysis and approximations, we construct a higher moment based stopping rule which is shown in numerical examples to perform more reliably and only slightly less efficiently than the second moment based stopping rule.

Publisher
16 p.
Series
Trita-NA, ISSN 0348-2952 ; 2012:7
Keyword
Monte Carlo methods; optimal stopping; sequential stopping rules; non-asymptotic
National Category
Probability Theory and Statistics Computer Science
Identifiers
urn:nbn:se:kth:diva-94109 (URN)
Note
QC 20120508Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2012-05-08Bibliographically approved
4. How accurate is molecular dynamics?
Open this publication in new window or tab >>How accurate is molecular dynamics?
Show others...
2012 (English)Report (Other academic)
Abstract [en]

Born-Oppenheimer dynamics is shown to provide an accurate approximation of time-independent Schrödinger observables for a molecular system with an electron spectral gap, in the limit of large ratio of nuclei and electron masses, without assuming that the nuclei are localized to vanishing domains. The derivation, based on a Hamiltonian system interpretation of the Schrödinger equation and stability of the corresponding hitting time Hamilton-Jacobi equation for non ergodic dynamics, bypasses the usual separation of nuclei and electron wave functions, includes caustic states and gives a different perspective on theBorn-Oppenheimer approximation, Schrödinger Hamiltonian systems and numerical simulation in molecular dynamics modeling at constant energy.

Publisher
47 p.
Series
TRITA-NA, ISSN 0348-2952 ; 2012:8
Keyword
Born-Oppenheimer approximation, WKB expansion, caustics, Fourier integral operators, Schrödinger operators
National Category
Mathematical Analysis Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-94125 (URN)
Funder
Swedish e‐Science Research Center
Note

QC 20120508

Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2016-12-22Bibliographically approved

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